Avoid single-commit strategy in doc-deploy actions

[jorgepiloto]

Problem

As per the issue raised in #1103, out doc-deploy actions must:

• Ensure that the deploy branch is an orphan branch
• Avoid having a unique commit in this branch

Previous issues introduce race conditions, large commit sizes, and long build times.

Furthermore, having multiple commits would allow us to roll-back a documentation in case we lost some data.

[RobPasMue]

There is a problem as stated in #1103 (comment) - we also want to avoid long gh-pages branch histories. I would recommend forcing a single commit from time to time. In my previous comment I suggest to do so whenever we do a release. But for the rest of the cases (PR/dev) we just commit diffs