Move ddev-platformsh to drud org and make official

[rfay]

"Official" ddev add-ons are in github.com/drud, and are maintained and tested.

But since this add-on is maintained and tested and has a bright future... can it be an "official" add-on?

Is there a way DDEV can define "offical" that is not "in the drud org"?

[rfay]

@fabpot in slack:

I would definitely make addon official. Moving it to the drud org sounds fine to me as well if needed.

[rfay]

This is easy to do and we can do it at any time. @lolautruche has a blog post coming out that would have to be adjusted, and obviously we have docs to fix.

I'm in the final throes of a DDEV release, so will not be able to pay much attention today, although I can do the move and so can @lolautruche - it's just "transfer ownership" of the repo from platformsh to drud orgs.

Things that need to be done after transfer:

• [x] Fix self-doc (README)
• [x] Change all platformsh/ddev-platformsh references in the repo
• [x] Do a new release
• [x] Fix DDEV docs that point to it (https://github.com/drud/ddev/pull/4460)
• [x] Fix docs.platformsh.com docs that point to it. (Incorporated into https://github.com/platformsh/platformsh-docs/pull/2754)

[rfay]

Done! Congrats all!