configure-projects: use '%{all_commits}' for squash commit template

This should at least prevent commit message contents from being lost on a squash merge where the user doesn't select a commit message. It may however be noisy if there are fixup commits involved.

Maybe should contain MR title and body as well?

Now only calls time.sleep() when saving a project, which should drastically shorten most runs. The previous call was unnecessary, since projects are already front-loaded and no requests are being made between projects.

Bug: T366624