Automatic merge from submit-queue (batch tested with PRs 51805, 51725, 50925, 51474, 51638)
Limit events accepted by API Server
**What this PR does / why we need it**:
This PR adds the ability to limit events processed by an API server. Limits can be set globally on a server, per-namespace, per-user, and per-source+object. This is needed to prevent badly-configured or misbehaving players from making a cluster unstable.
Please see https://github.com/kubernetes/community/pull/945.
**Release Note:**
```release-note
Adds a new alpha EventRateLimit admission control that is used to limit the number of event queries that are accepted by the API Server.
```
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