Transforms: Fix field matching in Format time, and add tpl var interpolation

[leeoniya]

previously, this transformer was displaying field names returned by getFieldDisplayName() but matching them using field.name, so they would not always match. this switches to using getFieldDisplayName() in both the editor and the matcher. also added a test.

also, it simplifies the transformer a bit and updates the test to account for the above logic.

additionally, it adds template variable interpolation for outputFormat so that subsequent "group by" transforms relying on the formatted field can be changed ad-hoc (part of the bigger epic: #25469)

this dashboard shows both the field matching fix and the interpolation:

formatTime-test.json

{
  "annotations": {
    "list": [
      {
        "builtIn": 1,
        "datasource": {
          "type": "grafana",
          "uid": "-- Grafana --"
        },
        "enable": true,
        "hide": true,
        "iconColor": "rgba(0, 211, 255, 1)",
        "name": "Annotations & Alerts",
        "type": "dashboard"
      }
    ]
  },
  "editable": true,
  "fiscalYearStartMonth": 0,
  "graphTooltip": 0,
  "id": 998,
  "links": [],
  "panels": [
    {
      "datasource": {
        "type": "grafana-testdata-datasource",
        "uid": "PD8C576611E62080A"
      },
      "description": "",
      "fieldConfig": {
        "defaults": {
          "color": {
            "mode": "thresholds"
          },
          "custom": {
            "align": "auto",
            "cellOptions": {
              "type": "auto"
            },
            "inspect": false
          },
          "mappings": [],
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "green",
                "value": null
              },
              {
                "color": "red",
                "value": 80
              }
            ]
          }
        },
        "overrides": []
      },
      "gridPos": {
        "h": 13,
        "w": 15,
        "x": 0,
        "y": 0
      },
      "id": 2,
      "options": {
        "cellHeight": "sm",
        "footer": {
          "countRows": false,
          "fields": "",
          "reducer": [
            "sum"
          ],
          "show": false
        },
        "showHeader": true
      },
      "pluginVersion": "11.0.0-pre",
      "targets": [
        {
          "datasource": {
            "type": "grafana-testdata-datasource",
            "uid": "PD8C576611E62080A"
          },
          "rawFrameContent": "[\n  {\n    \"schema\": {\n      \"refId\": \"Created\",\n      \"name\": \"issues\",\n      \"fields\": [\n        {\n          \"config\": {\n            \"displayName\": \"Key\"\n          },\n          \"labels\": {},\n          \"name\": \"key\",\n          \"type\": \"string\",\n          \"typeInfo\": {\n            \"frame\": \"string\",\n            \"nullable\": true\n          }\n        },\n        {\n          \"config\": {\n            \"displayName\": \"Created\"\n          },\n          \"labels\": {},\n          \"name\": \"created\",\n          \"type\": \"time\",\n          \"typeInfo\": {\n            \"frame\": \"time.Time\",\n            \"nullable\": true\n          }\n        }\n      ]\n    },\n    \"data\": {\n      \"values\": [\n        [\n          \"SF-1863\",\n          \"SF-1862\",\n          \"SF-1861\",\n          \"SF-1860\",\n          \"SF-1859\",\n          \"SF-1858\",\n          \"SF-1857\",\n          \"SF-1856\",\n          \"SF-1855\",\n          \"SF-1854\",\n          \"SF-1853\",\n          \"SF-1852\",\n          \"SF-1851\",\n          \"PTO-100\",\n          \"PTO-99\",\n          \"PS0029205-2\",\n          \"PS0026870-3\",\n          \"PS0026128-4\",\n          \"PS0025876-6\",\n          \"PS0025876-5\",\n          \"PS0025816-57\",\n          \"PS0025816-56\",\n          \"PS0025816-55\",\n          \"PS0025816-54\",\n          \"PS0025816-53\",\n          \"PS0025816-52\",\n          \"PS0024868-19\",\n          \"PS0024868-18\",\n          \"PS0023884-12\",\n          \"PS0023285-66\",\n          \"PS0022125-20\",\n          \"PS0020328-22\",\n          \"PS0020328-21\",\n          \"PS0018547-1\",\n          \"PS0018228-9\",\n          \"PS0018228-8\",\n          \"PS0016942-15\",\n          \"PS0016073-7\",\n          \"PS0011493-1\",\n          \"PS0009616-235\",\n          \"PS0005363-76\",\n          \"PS-8527\",\n          \"PS-8526\",\n          \"PS-8525\",\n          \"PS-8524\",\n          \"PS-8523\",\n          \"PS-8522\",\n          \"PS-8521\",\n          \"PS-8520\",\n          \"PS-8519\"\n        ],\n        [\n          1710177503710,\n          1709847191185,\n          1709840600792,\n          1709838120074,\n          1709836188764,\n          1709831316057,\n          1709761210192,\n          1709748960206,\n          1709740011528,\n          1709673236933,\n          1709672638016,\n          1709658801490,\n          1709618065051,\n          1709680274897,\n          1710195308883,\n          1709738721958,\n          1709652740992,\n          1709763222739,\n          1709824292784,\n          1709824220715,\n          1710195456846,\n          1709856404989,\n          1709856361641,\n          1709856325124,\n          1709848103773,\n          1709680345741,\n          1709846982308,\n          1709663202938,\n          1709636525756,\n          1709830139043,\n          1710127816144,\n          1710195423087,\n          1709757597091,\n          1710190370271,\n          1709663284954,\n          1709663260637,\n          1709763455433,\n          1710207024533,\n          1709781191294,\n          1709710333084,\n          1709836416655,\n          1710195544641,\n          1710188949035,\n          1710188860003,\n          1710188830916,\n          1710188781453,\n          1710188771454,\n          1710188692100,\n          1710188649941,\n          1709856465542\n        ]\n      ]\n    }\n  }\n]",
          "refId": "A",
          "scenarioId": "raw_frame"
        }
      ],
      "title": "Reproduced with embedded data",
      "transformations": [
        {
          "id": "formatTime",
          "options": {
            "outputFormat": "${format}",
            "timeField": "Created",
            "timezone": "",
            "useTimezone": true
          }
        },
        {
          "id": "groupBy",
          "options": {
            "fields": {
              "Created": {
                "aggregations": [],
                "operation": "groupby"
              },
              "Key": {
                "aggregations": [
                  "count"
                ],
                "operation": "aggregate"
              }
            }
          }
        }
      ],
      "type": "table"
    }
  ],
  "schemaVersion": 39,
  "tags": [
    "debug",
    "debug-timeseries"
  ],
  "templating": {
    "list": [
      {
        "current": {
          "selected": false,
          "text": "YYYY",
          "value": "YYYY"
        },
        "hide": 0,
        "includeAll": false,
        "multi": false,
        "name": "format",
        "options": [
          {
            "selected": true,
            "text": "YYYY",
            "value": "YYYY"
          },
          {
            "selected": false,
            "text": "YYYY-MM",
            "value": "YYYY-MM"
          },
          {
            "selected": false,
            "text": "YYYY-MM-DD",
            "value": "YYYY-MM-DD"
          },
          {
            "selected": false,
            "text": "YYYY-WW",
            "value": "YYYY-WW"
          }
        ],
        "query": "YYYY,YYYY-MM,YYYY-MM-DD,YYYY-WW",
        "queryValue": "",
        "skipUrlSync": false,
        "type": "custom"
      }
    ]
  },
  "time": {
    "from": "now-6h",
    "to": "now"
  },
  "timeRangeUpdatedDuringEditOrView": false,
  "timepicker": {},
  "timezone": "",
  "title": "formatTime-test",
  "uid": "bdfem2zo24n40a",
  "version": 9,
  "weekStart": ""
}

[baldm0mma]

Worked beautifully for me!