Add flagz endpoint for apiserver

[richabanker]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds a /flagz endpoint for kube-apiserver

Which issue(s) this PR fixes:

kubernetes/enhancements#4828

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Adds a /flagz endpoint for kube-apiserver endpoint

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

• KEP : https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/4828-component-flagz/README.md

Snippet of response returned by

curl -k --cert /etc/kubernetes/pki/apiserver-kubelet-client.crt --key /etc/kubernetes/pki/apiserver-kubelet-client.key https://localhost:6443/flagz

----------------------------
title: apiserver flagz
description: flags enabled in apiserver
warning: This endpoint is not meant to be machine parseable and is for debugging purposes only.
----------------------------

advertise-address=192.168.8.2
contention-profiling=false
enable-priority-and-fairness=true
profiling=true
authorization-mode=[Node,RBAC]
authorization-webhook-cache-authorized-ttl=5m0s
authorization-webhook-cache-unauthorized-ttl=30s
authorization-webhook-version=v1beta1
default-watch-cache-size=100
delete-collection-workers=1
enable-garbage-collector=true
encryption-provider-config-automatic-reload=false
etcd-cafile=/etc/kubernetes/pki/etcd/ca.crt
etcd-certfile=/etc/kubernetes/pki/apiserver-etcd-client.crt
etcd-compaction-interval=5m0s
etcd-count-metric-poll-period=1m0s
etcd-db-metric-poll-interval=30s
etcd-healthcheck-timeout=2s
etcd-keyfile=/etc/kubernetes/pki/apiserver-etcd-client.key
etcd-prefix=/registry
etcd-readycheck-timeout=2s
etcd-servers=[https://127.0.0.1:2379]
lease-reuse-duration-seconds=60
storage-media-type=application/vnd.kubernetes.protobuf
watch-cache=true

[richabanker]

/remove-sig cli
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/remove-area kubelet
/remove-area kube-proxy
/remove-area kubectl

[richabanker]

/remove-sig apps
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/remove-sig etcd
/remove-sig network
/remove-sig node
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/remove-sig storage
/remove-sig testing
/remove-sig windows

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: richabanker
Once this PR has been reviewed and has the lgtm label, please ask for approval from dgrisonnet and additionally assign sttts for approval. For more information see the Kubernetes Code Review Process.

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Needs approval from an approver in each of these files:

• cmd/kube-apiserver/OWNERS
• pkg/controlplane/OWNERS
• staging/src/k8s.io/apiserver/OWNERS
• staging/src/k8s.io/component-base/zpages/OWNERS

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[k8s-triage-robot]

This PR may require API review.

If so, when the changes are ready, complete the pre-review checklist and request an API review.

Status of requested reviews is tracked in the API Review project.

[k8s-ci-robot]

@richabanker: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubernetes-verify	7d6679c	link	true	/test pull-kubernetes-verify
pull-kubernetes-integration	7d6679c	link	true	/test pull-kubernetes-integration
pull-kubernetes-e2e-gce-cos-alpha-features	7d6679c	link	false	/test pull-kubernetes-e2e-gce-cos-alpha-features

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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