Support auto generation of Channels Subscription 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 Channels subscriptions identity (from SubscriberStatus)
  • expose the service accounts name in .status.auth.serviceAccountName

[Priyansurout]

/assign

[xiangpingjiang]

hello @creydr
Why this issue moved to Draft?
Is it ready for grab?

[creydr]

Because we need to recheck on this if it's needed, after 7223 is done

[creydr]

Done in #7223