webhooks,aggregation: add metrics to count certs with SHA1 signatures

[stlaz]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Extends the certificate attribute deprecation RoundTrippers wrapper with
a checker that counts certificates with sha-1 signatures in server responses.

Non-root non-self-signed SHA-1 certificate signatures were deprecated in
Golang 1.18

Which issue(s) this PR fixes:
#108940

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

(this release note includes log and audit annotation prefixes added in #109107)

Kubernetes 1.24 is built with go1.18, which will no longer validate certificates signed with a SHA-1 hash algorithm by default. See https://golang.org/doc/go1.18#sha1 for more details. If you are using certificates like this in admission or conversion webhooks or in aggregated API servers, you should replace those certificates as soon as possible, since SHA-1 is no longer considered secure. If you cannot replace those certificates before upgrading to Kubernetes 1.24, or do not know whether you have certificates like this, you can:
* temporarily re-enable honoring SHA-1 certificates by setting the `GODEBUG=x509sha1=1` environment variable when starting kube-apiserver
* monitor `apiserver_kube_aggregator_x509_insecure_sha1_total` and `apiserver_webhooks_x509_insecure_sha1_total` metrics in `kube-apiserver`, added in v1.24; non-zero values for these metrics indicate connections to aggregated API servers or webhooks are encountering SHA-1 certificates, and will stop working in the future when go removes SHA-1 support completely
* if metrics indicate SHA-1 certificates are being encountered, information about the specific hosts serving those certificates is available in the kube-apiserver log, containing `invalid-cert.kubernetes.io`, and in the kube-apiserver audit log, with an `insecure-sha1.invalid-cert.kubernetes.io/$hostname` audit annotation

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[Other doc]: https://tip.golang.org/doc/go1.18#sha1

[k8s-ci-robot]

Hi @stlaz. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[MadhavJivrajani]

/ok-to-test
/priority critical-urgent

[MadhavJivrajani]

/remove-priority critical-urgent
/priority important-soon
(oops!)

[stlaz]

/test pull-kubernetes-integration
the logs say all the tests passed but the status still seems red here

[MadhavJivrajani]

@liggitt fyi

[logicalhan]

/lgtm
(from a metrics side)

[liggitt]

/lgtm
/approve
/hold cancel
/triage accepted

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt, stlaz

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Needs approval from an approver in each of these files:

• staging/src/k8s.io/apiserver/OWNERS [liggitt]
• staging/src/k8s.io/kube-aggregator/OWNERS [liggitt]

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[liggitt]

I updated the release note to reference the go release notes, describe use of GODEBUG, the new metrics, and the kube-apiserver log.

[liggitt]

I also marked it as action-required