[WIP] Add filtering label to secret and enable secret informer filtering by default

[nak3]

Changes

Currently users have to set ENABLE_SECRET_INFORMER_FILTERING_BY_CERT_UID to enable secret informer filtering.
It has a big pain that they have to add a label to their every single secret on their DomainMapping's BYO certs.

This patch changes the controller to add the label to the secret specified by DomainMapping.
As a consequence, it can enable ENABLE_SECRET_INFORMER_FILTERING_BY_CERT_UID by default.

/kind enhancement

Release Note

Kourier controller injects labels (`networking.internal.knative.dev/certificate-uid: <secret_name>`) to the secret used by auto-tls or DomainMapping's BYO certs.
It make possible to enables secret informer filtering (enabled via `ENABLE_SECRET_INFORMER_FILTERING_BY_CERT_UID` for now) by defalut.

TODO:

• update unit test

[knative-prow]

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[codecov]

Codecov Report

Merging #1084 (b98dd66) into main (2a2db6d) will decrease coverage by 0.43%.
Report is 19 commits behind head on main.
The diff coverage is 45.00%.

@@            Coverage Diff             @@
##             main    #1084      +/-   ##
==========================================
- Coverage   80.00%   79.57%   -0.43%     
==========================================
  Files          18       18              
  Lines        1430     1449      +19     
==========================================
+ Hits         1144     1153       +9     
- Misses        229      237       +8     
- Partials       57       59       +2     

Files Changed	Coverage Δ
pkg/generator/ingress_translator.go	82.00% <45.00%> (-2.06%)	⬇️

[nak3]

@skonto @dprotaso Could you please take a look if this approach is alright? I will add tests if no problem.
It is related to #862 knative-extensions/net-istio#920

[skonto]

So we are trying to make the UX easier, non-breaking and we add the label ourselves.
Are there any other secrets that might need the same?

[nak3]

Other secrets are deployed by us and so we have already added the label like https://github.com/knative/serving/blob/main/config/core/300-secret.yaml#L34 by default. So we don't need it.

[nak3]

So, is it okay for this approach?

[knative-prow-robot]

PR needs rebase.

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[nak3]

Closing due to no feedback.