[NATS] Add connection data stream metric types

[gpop63]

What does this PR do?

Add metric types for connection data stream fields.

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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• Start Time: 2023-10-10T22:20:27.131+0000

• Duration: 31 min 44 sec

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Test	Results
Failed	0
Passed	31
Skipped	2
Total	33

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[gpop63]

/test

[gpop63]

After fixing aggregation type for counters.

[gpop63]

Rollover test

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

Mappings

 "nats": {
          "properties": {
            "connection": {
              "properties": {
                "idle_time": {
                  "type": "long",
                  "time_series_metric": "gauge"
                },
                "in": {
                  "properties": {
                    "bytes": {
                      "type": "long",
                      "time_series_metric": "counter"
                    },
                    "messages": {
                      "type": "long",
                      "time_series_metric": "counter"
                    }
                  }
                },
                "name": {
                  "type": "keyword",
                  "time_series_dimension": true
                },
                "out": {
                  "properties": {
                    "bytes": {
                      "type": "long",
                      "time_series_metric": "counter"
                    },
                    "messages": {
                      "type": "long",
                      "time_series_metric": "counter"
                    }
                  }
                },
                "pending_bytes": {
                  "type": "long",
                  "time_series_metric": "gauge"
                },
                "subscriptions": {
                  "type": "long",
                  "time_series_metric": "gauge"
                },
                "uptime": {
                  "type": "long",
                  "time_series_metric": "counter"
                }
              }
            },

[agithomas]

Can you re-confirm this is Gauge, not counter?

[gpop63]

You're right, it's a counter.

[agithomas]

LGTM keeping TSDB scope.

[elasticmachine]

Package nats - 1.3.6 containing this change is available at https://epr.elastic.co/search?package=nats