RP: Read the Docs

[mtitov]

Review triggers that launch building RTD pages

• RTD version stable - should be triggered by release;
• RTD version devel - should be triggered manually (to test RTD before the release).

[andre-merzky]

The RTD project got re-enabled, and PR #3245 implements building docs in a GH action. Alas, that also takes too long (>2hrs for getting_started.ipynb). What now?

[mtitov]

Issues with RTD were resolved,
probably, it is worth checking the set of warnings that were printed out in the logs (in a separate PR)

• updated tutorials and docs #3296 - updates tutorials (no hanging processes after each one is executed)
• fix RTD build #3245 - to be rediscussed with Andre

Ticket can be closed

[mtitov]

@andre-merzky @mturilli Should we close (without merging) a corresponding PR (#3245 )? or we can merge only .github/workflows/rtd.yml since it is a new config, so to preserve it, but without activating it? (not sure about changes toward existing files/modules, maybe that could stay within PR only?)