chore(set-identifier): expand annotation docs and add test coverage

[ivankatliarchuk]

What does it do ?

• Added test coverage for set identifier, to make sure we have a baseline
• Updated documentation with examples, notes and cross-reference

Follow-up:

• enchance docs to auto-document which sources supports set-identifier docs(sources): surface provider-specific annotations support in documentation #6231
• all sources to support set-identifier
• review edge-cases in aws provider

Motivation

Relates #4494

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

[coveralls]

Pull Request Test Coverage Report for Build 23110656995

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 79.676%

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Totals
Change from base Build 23098157121:	0.0%
Covered Lines:	16599
Relevant Lines:	20833

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💛 - Coveralls

[mloiseleur]

/lgtm

[ivankatliarchuk]

/test pull-external-dns-unit-test

[ivankatliarchuk]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ivankatliarchuk

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