Automatic merge from submit-queue (batch tested with PRs 65256, 64236, 64919, 64879, 57932). 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>.
Cancellable leader election
**What this PR does / why we need it**:
Adds ability to cancel leader election. Useful in integration tests where the whole app is started and stopped in each test.
**Special notes for your reviewer**:
I used the `context` package - it is impossible/hard to achieve the same behaviour with just channels without spawning additional goroutines but it is trivial with `context`. See `acquire()` and `renew()` methods.
**Release note**:
```release-note
NONE
```
/kind enhancement
/sig api-machinery
571b9beac5