dont overwrite metadata in rds and dimension in cloudwatch

[aspacca]

Bug

What does this PR do?

Ensure that dimensions and rds metadata from cloudwatch metric are not overwritten

Why is it important?

It was reported a case of mismatching metadata in RDS metrics between aws.dimensions.DBInstanceIdentifier and aws.rds.db_instance.identifier

Changes in this PR will prevent to set the metadata and dimensions multiple time if they are already set for a specific event

Checklist

• My code follows the style guidelines of this project
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• [ ]

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[mergify]

This pull request does not have a backport label. Could you fix it @aspacca? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

Pinging @elastic/integrations (Team:Platforms)

[elasticmachine]

❕ Build Aborted

There is a new build on-going so the previous on-going builds have been aborted.

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Build stats

• Reason: Aborted from #2

• Start Time: 2021-11-23T13:02:08.534+0000

• Duration: 8 min 39 sec

• Commit: 54451ae

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[endorama]

Can we add a test around this? Or shouldn't this be found out by the tests already?

[aspacca]

@endorama sure, we can add a test mocking wrong metadata and assuring only the first one will be set

[aspacca]

closing in favour of #29106

[elasticmachine]

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

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