Moved all flag code from `staging/src/k8s.io/apiserver/pkg/util/[flag|globalflag]` to `component-base/cli/[flag|globalflag]` except for the term function because of unwanted dependencies.
Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Remove deprecated --require-kubeconfig flag, remove default --kubeconfig value
**What this PR does / why we need it**:
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes#41161
**Special notes for your reviewer**:
**Release note**:
```release-note
Remove deprecated --require-kubeconfig flag, remove default --kubeconfig value
```
This feature gate was redundant with the `--config` flag, which already
enables/disables loading Kubelet config from a file.
Since the gate guarded an alpha feature, removing it is not a violation
of our API guidelines.
Some stuff in `kubernetes/test-infra` currently sets the gate,
so removing will be a 3 step process:
1. This PR, which makes the gate a no-op.
2. Stop setting the gate in `kubernetes/test-infra`.
3. Completely remove the gate.
