Automatic merge from submit-queue (batch tested with PRs 45247, 45810, 45034, 45898, 45899)

Apiregistration v1alpha1→v1beta1

Promoting apiregistration api from v1alpha1 to v1beta1.

API Registration is responsible for registering an API `Group`/`Version` with
another kubernetes like API server. The `APIService` holds information
about the other API server in `APIServiceSpec` type as well as general
`TypeMeta` and `ObjectMeta`. The `APIServiceSpec` type have the main
configuration needed to do the aggregation. Any request coming for
specified `Group`/`Version` will be directed to the service defined by
`ServiceReference` (on port 443) after validating the target using provided
`CABundle` or skipping validation if development flag `InsecureSkipTLSVerify`
is set. `Priority` is controlling the order of this API group in the overall
discovery document.
The return status is a set of conditions for this aggregation. Currently
there is only one condition named "Available", if true, it means the
api/server requests will be redirected to specified API server.

```release-note
API Registration is now in beta.
```