Wiki placeholder commit messages for Web UI could be better

Description

When editing a wiki page from the UI (as opposed to checking the wiki repo out and editing and committing there) the commit message always seems to be a copy of the previous commit message used. So the only time the commit message is actually useful is when it is set manually during a git commit on a checked out wiki repo.

This is with CE 8.16.5, btw

Proposal

When editing a wiki page in the UI set the commit message to something like 'page XXX edited'. This is at least more helpful than having a commit message that has nothing to do with the actual page being edited, as is now the case.

Links / references

Documentation blurb

(Write the start of the documentation of this feature here, include:

1. Why should someone use it; what's the underlying problem.
2. What is the solution.
3. How does someone use this

During implementation, this can then be copied and used as a starter for the documentation.)