Automatic merge from submit-queue (batch tested with PRs 45100, 45152, 42513, 44796, 45222)

[Federation] Generate the secret name in kubefed join.

Addresses part of #42324. A follow-up PR will address annotating Federation resources.

```release-note
Remove the `--secret-name` flag from `kubefed join`, instead generating the secret name arbitrarily.
```