#1221 Prepare Git repo for v9.0 development

• Best to review per commit.
• I've just followed our documented steps. No surprises.
• This for now targets the 1171-release-notes-v8.0 branch. Once the merge request for that one is merged, this will automatically be re-targetted to develop. This is a draft for now, to be merged only once %v8.0 has been released.

Closes #1221 (closed)