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apiserver: change default reconciler to LeaseEndpoint

**What this PR does / why we need it**:

Graduates the lease-endpoint-reconciler flag to beta, and defaults the endpoint reconciler to LeaseEndpoint instead of MasterCount.

- [x] Default Lease Endpoint Reconciler to on

**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 #57617

**Special notes for your reviewer**:

**Release note**:

```release-note
kube-apiserver: `--endpoint-reconciler-type` now defaults to `lease`. The `master-count` reconciler is deprecated and will be removed in 1.13.
```