* Create docker-build-and-push.yml
* Switched to using official Docker buildx action
* Added comment to docker-build-and-push.yml
In case something needs to be tweaked in the future, the link
contains some examples and explanations which would be useful
* Run only on release (and produce release tags)
As this workflow takes quite a lot of time, and [pushing to master happens frequently](https://github.com/matrix-org/dendrite/pull/1613#issuecomment-746086980), the container will now only be built when a release is created, and the builds will also be correctly tagged.
* Add latest tag, test at neilalexander/dendrite*
Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>
