Make docker gitea/gitea:v1.16-dev etc refer to the latest build on that branch (#18551) (#18569)

Backport #18551

(Backporting this will enable this target to create 1.16-dev)

One of the problems with our current docker tagging is that although we
have strict version tags, latest and dev we do not have a way for docker
users to track the current release branch. This PR simply suggests that
we use the 1.x-dev tag for these and we build and push these. This will
give users who want or need unreleased bug fixes the option of tracking
the pre-release version instead of simply jumping to dev.

(Also contains backport for #18573)

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: KN4CK3R <admin@oldschoolhack.me>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

.drone.yml

@@ -1086,6 +1086,7 @@ steps:
 trigger:
   ref:
   - refs/heads/main
+  - "refs/heads/release/v*"
   event:
     exclude:
     - cron