Tracing: Correct tags for each span are shown

[ivanahuckova]

What this PR does / why we need it:
We were showing wrong tags in spans. More context here: https://raintank-corp.slack.com/archives/CPXKS6FB5/p1634297506265900

To fix this, we have decided to have 1-1 relationship between span and process. We are using spanID as a key as it should be unique within the trace.

Which issue(s) this PR fixes:

Fixes #40625

Special notes for your reviewer:

I have added test for this. You can also upload this trace to see the difference (after JSON upload fix is merged #41455):

{
  "batches": [
    {
      "resource": {
        "attributes": [
          {
            "key": "service.name",
            "value": {
              "stringValue": "frontend"
            }
          },
          {
            "key": "host.name",
            "value": {
              "stringValue": "frontend-1"
            }
          }
        ]
      },
      "instrumentationLibrarySpans": [
        {
          "instrumentationLibrary": {},
          "spans": [
            {
              "traceId": "AAAAAAAAAACEiiIwxeKP9A==",
              "spanId": "hIoiMMXij/Q=",
              "name": "frontend",
              "startTimeUnixNano": "1634296766948000000",
              "endTimeUnixNano": "1634296767232000000",
              "attributes": [],
              "status": {}
            }
          ]
        }
      ]
    },
    {
      "resource": {
        "attributes": [
          {
            "key": "service.name",
            "value": {
              "stringValue": "querier"
            }
          },
          {
            "key": "host.name",
            "value": {
              "stringValue": "querier-1"
            }
          }
        ]
      },
      "instrumentationLibrarySpans": [
        {
          "instrumentationLibrary": {},
          "spans": [
            {
              "traceId": "AAAAAAAAAACEiiIwxeKP9A==",
              "spanId": "MdmmKDpzjyE=",
              "parentSpanId": "hIoiMMXij/Q=",
              "name": "span from querier-1",
              "startTimeUnixNano": "1634296766990000000",
              "endTimeUnixNano": "1634296767167000000",
              "attributes": [],
              "status": {}
            }
          ]
        }
      ]
    },
    {
      "resource": {
        "attributes": [
          {
            "key": "service.name",
            "value": {
              "stringValue": "querier"
            }
          },
          {
            "key": "host.name",
            "value": {
              "stringValue": "querier-2"
            }
          }
        ]
      },
      "instrumentationLibrarySpans": [
        {
          "instrumentationLibrary": {},
          "spans": [
            {
              "traceId": "AAAAAAAAAACEiiIwxeKP9A==",
              "spanId": "mwJYmrj4CBs=",
              "parentSpanId": "hIoiMMXij/Q=",
              "name": "span from querier-2",
              "startTimeUnixNano": "1634296767133000000",
              "endTimeUnixNano": "1634296767147000000",
              "attributes": [],
              "status": {}
            }
          ]
        }
      ]
    }
  ]
}