[NATS] Add route data stream metric types

[gpop63]

What does this PR do?

Adds route data stream metric types.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Relates NATS TSDB Enablement #7745

Screenshots

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Build stats

• Start Time: 2023-10-12T12:35:22.833+0000

• Duration: 29 min 2 sec

Test stats 🧪

Test	Results
Failed	0
Passed	31
Skipped	2
Total	33

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Methods	100.0% (29/29)	💚 8.889
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[gpop63]

Rollover test

{
  "acknowledged": true,
  "shards_acknowledged": true,
  "old_index": ".ds-metrics-nats.route-default-2023.09.21-000001",
  "new_index": ".ds-metrics-nats.route-default-2023.09.21-000002",
  "rolled_over": true,
  "dry_run": false,
  "conditions": {}
}

Mappings

"nats": {
          "properties": {
            "route": {
              "properties": {
                "in": {
                  "properties": {
                    "bytes": {
                      "type": "long",
                      "time_series_metric": "counter"
                    },
                    "messages": {
                      "type": "long",
                      "time_series_metric": "counter"
                    }
                  }
                },
                "ip": {
                  "type": "ip",
                  "time_series_dimension": true
                },
                "out": {
                  "properties": {
                    "bytes": {
                      "type": "long",
                      "time_series_metric": "counter"
                    },
                    "messages": {
                      "type": "long",
                      "time_series_metric": "counter"
                    }
                  }
                },
                "pending_size": {
                  "type": "long",
                  "time_series_metric": "gauge"
                },
                "port": {
                  "type": "long",
                  "time_series_dimension": true
                },
                "remote_id": {
                  "type": "keyword",
                  "time_series_dimension": true
                },
                "subscriptions": {
                  "type": "long",
                  "time_series_metric": "gauge"
                }
              }
            },

[agithomas]

LGTM from TSDB perspective

[agithomas]

Suggested change

	- description: Added metric_type mapping to route data stream.
	- description: Add metric_type mapping to route data stream.

[elasticmachine]

Package nats - 1.3.9 containing this change is available at https://epr.elastic.co/search?package=nats