feat(gslb): Add support to filter out non delegated zones

[Piroddi]

After fetching the servers from either Ingress, HttpRoute or VirtualService the gslb reconciliation will now filter only the hosts that have been delegated to k8gb.

This allows users to use a single resource to define both k8gb hosts and non k8gb hosts.

Fixes: #2183

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[ytsarev]

Thanks a lot for the contribution!

High level looks great, can you please cover the impementation with unit test(s)?

[Piroddi]

Thanks a lot for the contribution!

High level looks great, can you please cover the impementation with unit test(s)?

Thanks @ytsarev

Currently the changes are inline of the reconciler, so a test would require a full integration test and mocking of the Delegation Zones in the config.

I could move this filtering logic out into a separate function and add a unit test on the function itself?

[ytsarev]

@Piroddi

I could move this filtering logic out into a separate function and add a unit test on the function itself?

yes, i think isolated unit test is enough for this change 👍

[ytsarev]

Thanks a lot for the contribution and the test coverage! 💪