Document builds: Record Last Triggered Image ID in status

Docs Impact

Release note is already covered in https://github.com/openshift/openshift-docs/pull/33934

Next, I should review the API docs that Jason B is regenerating on Tuesday, 6/29, and add a deprecation notice, if needed. I should also consider updating the godoc in plain text, with the content I add to the generated API docs, so that the next time Jason regenerates the API docs, that added content doesn't get lost.  

Rolfe, see your comments below.