[STAN] Add stats data stream dimensions

[gpop63]

What does this PR do?

Adds stats data stream dimensions.

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 STAN TSDB Enablement #7859

Screenshots

The dashboard for STAN metrics seems to be broken (this has to be addressed). I recreated the lenses just for visualization and data validation.

[elasticmachine]

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• Start Time: 2023-10-29T23:39:30.265+0000

• Duration: 20 min 37 sec

Test stats 🧪

Test	Results
Failed	0
Passed	17
Skipped	0
Total	17

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[gpop63]

TSDB testing kit output:

Testing data stream metrics-stan.stats-default.
Index being used for the documents is .ds-metrics-stan.stats-default-2023.10.18-000001.
Index being used for the settings and mappings is .ds-metrics-stan.stats-default-2023.10.18-000001.

The time series fields for the TSDB index are: 
        - dimension (11 fields):
                - agent.id
                - cloud.account.id
                - cloud.availability_zone
                - cloud.instance.id
                - cloud.provider
                - cloud.region
                - container.id
                - host.name
                - service.address
                - stan.cluster.id
                - stan.server.id
        - counter (2 fields):
                - stan.stats.bytes
                - stan.stats.messages
        - gauge (3 fields):
                - stan.stats.channels
                - stan.stats.clients
                - stan.stats.subscriptions
        - routing_path (11 fields):
                - agent.id
                - cloud.account.id
                - cloud.availability_zone
                - cloud.instance.id
                - cloud.provider
                - cloud.region
                - container.id
                - host.name
                - service.address
                - stan.cluster.id
                - stan.server.id

Index tsdb-index-enabled successfully created.

Copying documents from .ds-metrics-stan.stats-default-2023.10.18-000001 to tsdb-index-enabled...
All 1459 documents taken from index .ds-metrics-stan.stats-default-2023.10.18-000001 were successfully placed to index tsdb-index-enabled.

[agithomas]

LGTM!

[elasticmachine]

Package stan - 1.3.8 containing this change is available at https://epr.elastic.co/search?package=stan