rethink metadata (author and commit) for subgraph action (publish; delete; promote)

> Originally this was a comment in https://github.com/graphql-hive/console/pull/8031 that was out of scope there.

We have a way to associate a author and commit with a schema publish (and even enforce these to be passed). We should also allow customising the author and commit being used for all of these actions and make them fully optional, as some users find it an annoyance having to pass these along.