docs(sources): surface provider-specific annotations support in documentation

[ivankatliarchuk]

What does it do ?

• Added // +externaldns:source:provider-specific=true|false annotation to every source struct in source/, based on whether the source calls annotations.ProviderSpecificAnnotations
• Extended the doc generator (internal/gen/docs/sources/main.go) with a new annotationProviderSpecific constant
• Added tests to capture where provider specific annotations supported/not-supporte for ALL sources, that currently missing it

Follow-up

• add support for provider specific annotations for sources that currently do not support it
• TTL config in auto-docs

Motivation

Sources differ in whether they support provider-specific properties (e.g. AWS routing policies, Cloudflare proxying, SCW/webhook extensions). This distinction was implicit and invisible — there was no machine-readable way to know which sources honour provider-specific annotations without reading the source code. Surfacing this as a structured annotation makes it queryable by tooling and visible in the generated documentation, helping users understand which sources can carry provider-specific configuration to their DNS provider.

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 23285862349

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 316 unchanged lines in 22 files lost coverage.
• Overall coverage increased (+0.01%) to 78.159%

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Files with Coverage Reduction	New Missed Lines	%
fake.go	1	96.23%
empty.go	1	75.0%
connector.go	2	83.33%
pod.go	5	95.61%
node.go	6	90.4%
f5_virtualserver.go	8	79.79%
contour_httpproxy.go	8	84.33%
istio_gateway.go	8	88.55%
f5_transportserver.go	8	78.65%
openshift_route.go	9	83.59%

Totals
Change from base Build 23251413358:	0.01%
Covered Lines:	16465
Relevant Lines:	21066

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💛 - Coveralls

[ivankatliarchuk]

/test pull-external-dns-unit-test

[mloiseleur]

/lgtm

[ivankatliarchuk]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ivankatliarchuk

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