Support auto generation of ApiServerSource identity service account and expose in `AuthStatus`

[creydr]

Problem

As the Eventing OIDC feature track describes, the AuthStatus is meant to provide the generated service account name in the resource status.

After #7173 is done, we should:

• when the feature flag (see Add authentication.oidc feature flag #7174) is disabled:
  • no change in behavior
• when the feature flag (see Add authentication.oidc feature flag #7174) is enabled:
  • create the service account for the ApiServerSource identity
  • expose the service accounts name in .status.auth.serviceAccountName

[aliok]

hi @creydr

I see you've added help-wanted label to this issue. If you think this is a good good-first-issue, can you:

• Comment with /good-first-issue?
• Add clear instructions (including code pointers) about how this issue can be resolved?

[Leo6Leo]

/assign

[creydr]

#7299 and #7316 show how this was done for the Trigger and could help to get started with this.

/good-first-issue

[knative-prow]

@creydr:
This request has been marked as suitable for new contributors.

Please ensure the request meets the requirements listed here.

If this request no longer meets these requirements, the label can be removed
by commenting with the /remove-good-first-issue command.

Details

In response to this:

#7299 and #7316 show how this was done for the Trigger and could help to get started with this.

/good-first-issue

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