WIP chore(source): istio index services

[ivankatliarchuk]

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What does it do ?

note; to review after release

Indexers are way waster then listers, the difference could be 10x times with a cost of +~10% memory usage(for indexes)

Motivation

• previous PR https://github.com/kubernetes-sigs/external-dns/pull/5536
• previous PR https://github.com/kubernetes-sigs/external-dns/pull/5466
• opened PR https://github.com/kubernetes-sigs/external-dns/pull/5473#issuecomment-2911576025

TODO:

• share syntetic results
• share results for real cluster

More

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