Update Function

Update an existing function's metadata, code, or both. Also the publish path: set function.published_commit_id and include "published_commit_id" in update_mask to make a commit the default runnable version. To push a new code commit, set content (and optionally commit_message); this is independent of update_mask, since commits are versioned separately from function metadata. A single request cannot publish the commit it just created, since published_commit_id is validated against existing commits before content is committed: publishing new code takes two calls, push then publish with the returned commit.id.