Make all submodules have absolute URLs -- for 8.8

The relative URLs were a workaround to let most contributors fork from Github due to a weakness in the haskell.org server.

This workaround is no longer needed. And relative submodule URLs are an impediment to forking which makes contributions harder than they should be.

The URLs are chosen to clone from https, because this makes sure that anybody, even not a registered Gitlab user, can clone a fork recursively.

(cherry picked from commit a76b233d)

• are either individually buildable or squashed
• have commit messages which describe what they do (referring to Notes and tickets using #NNNN syntax when appropriate)
• have added source comments describing your change. For larger changes you likely should add a Note and cross-reference it from the relevant places.
• add a testcase to the testsuite.
• replace this message with a description motivating your change

If you have any questions don't hesitate to open your merge request and inquire in a comment. If your patch isn't quite done yet please do add prefix your MR title with WIP:.