Add doc for ACR endpoints support

### What would you like to be added?

We recently added support for users to configure endpoints for ACR, related doc should be added.
https://github.com/ratify-project/ratify/pull/2069#discussion_r1929919685

### Anything else you would like to add?

_No response_

### Are you willing to submit PRs to contribute to this feature?

- [x] Yes, I am willing to implement it.