[release-1.8] Certificate controller to only watch secrets with a label

[knative-prow-robot]

This is an automated cherry-pick of #225

Certificate controller to only watch secrets with a label

[evankanderson]

/lgtm /approve

[codecov[bot]]

Codecov Report

Merging #253 (60eaa63) into release-1.8 (3e2f878) will decrease coverage by 9.83%. The diff coverage is 35.39%.

@@               Coverage Diff               @@
##           release-1.8     #253      +/-   ##
===============================================
- Coverage        82.66%   72.83%   -9.83%     
===============================================
  Files               21       23       +2     
  Lines             1090     1377     +287     
===============================================
+ Hits               901     1003     +102     
- Misses             148      317     +169     
- Partials            41       57      +16     

Impacted Files	Coverage Δ
pkg/certificates/reconciler/reconciler.go	27.96% <27.96%> (ø)
pkg/certificates/reconciler/controller_impl.go	62.50% <62.50%> (ø)
pkg/certificates/reconciler/controller.go	92.85% <100.00%> (+0.54%)	:arrow_up:
pkg/network/base_connection.go	89.28% <0.00%> (+2.67%)	:arrow_up:

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[knative-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: evankanderson, knative-prow-robot

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/knative-sandbox/control-protocol/blob/release-1.8/OWNERS)~~ [evankanderson] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[evankanderson]

Based on report here: https://cloud-native.slack.com/archives/C04LMU0AX60/p1674692609842299

[dprotaso]

I think the code coverage is broken for this branch unsure why

/override codecov/patch /override codecov/project

[knative-prow[bot]]

@dprotaso: Overrode contexts on behalf of dprotaso: codecov/patch, codecov/project

In response to [this](https://github.com/knative-sandbox/control-protocol/pull/253#issuecomment-1430121263): >I think the code coverage is broken for this branch unsure why > >/override codecov/patch >/override codecov/project Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.