Add CI to build docker images on releases (#836)

* Fix the url of the fetched file

* Fix binary in the GPG check

* Add docker build

* Import GPG pub keys

* Copy missing binaries

* Checkout first

* Add missing mkdir

* Set bin as executable

* Fix exec flag earlier

* Fix docker calls

* Fix version parsing

* Fix image names

* Cleanup

* Fix ENV issue

* Only allow user keys on pre-releases

* Add Docker Hub token and enable pushing

* Make Docker owner configurable via secrets

* Fix owner

* Remove duplicate secret

cumulus/.github/workflows/release-99_bot-announce.yml

@@ -1,4 +1,4 @@
-name: Pushes release notes to a Matrix room
+name: Release - Pushes release notes to a Matrix room
 on:
   release:
     types: