[NATS] Add subscriptions data stream dimensions

[gpop63]

What does this PR do?

Adds subscriptions 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 NATS TSDB Enablement #7745

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• Start Time: 2023-10-12T16:01:48.069+0000

• Duration: 31 min 6 sec

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Test	Results
Failed	0
Passed	31
Skipped	2
Total	33

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚
Classes	100.0% (1/1)	💚
Methods	100.0% (29/29)	💚
Lines	95.522% (192/201)	👍
Conditionals	100.0% (0/0)	💚

[agithomas]

LGTM from the point of view of TSDB.

[agithomas]

Suggested change

	- description: Added dimensions mappings and ECS fields to subscriptions data stream.
	- description: Add dimensions mappings and ECS fields to subscriptions data stream.

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Package nats - 1.4.2 containing this change is available at https://epr.elastic.co/search?package=nats