proto annotation for a method that supports partial update

[toumorokoshi]

Context:

no I don't think so - follow-up issue? 

One could argue that the existence of an update_mask field is the proof that partial update is supported..

Originally posted by @toumorokoshi in https://github.com/aep-dev/aep.dev/pull/210#discussion_r1729448879

[rambleraptor]

I meant something totally different in my comment. I responded in the PR comment, but tl;dr, let's close this issue.