It became clear in our standup today that this fields name and documentation are not clear. I think we at least need to update the docs to say that this is the SHA of the commit landed in the language repo and NOT the commit in googleapis. Elsewhere we use the word source to reference googleapis today so this is causing some confusion.

Ref: https://github.com/googleapis/librarian/blob/main/doc/language-onboarding.md#release-init