chore: create a master tag on docker hub (#479)

* chore: rename master tag

* chore: also include staging tag

Author: r4mmer

scripts/github/docker.py

@@ -47,6 +47,7 @@ def prep_tags(environ: Dict):
         # A push to master creates a staging tag
         tags.add(base_ecr_tag + 'staging-{}-{}'.format(sha, timestamp))
         tags.add(base_dockerhub_tag + 'staging-{}-{}'.format(sha, timestamp))
+        tags.add(base_dockerhub_tag + 'master')
     else:
         # A push to any other branch creates a dev tag
         # XXX: We currently do not run on other branches