Improve drone CI to handle tags and build latest image on main branch only.

.drone.yml

@@ -3,7 +3,7 @@ type: docker
 name: build-docker-image
 
 steps:
-- name: docker
+- name: docker-latest
   image: plugins/docker
   settings:
     repo: madeorsk/clang-llvm-meson-buildtools
@@ -11,3 +11,19 @@ steps:
       from_secret: docker_registry_username
     password:
       from_secret: docker_registry_password
+  when:
+    branch:
+      - main
+
+- name: docker-tag
+  image: plugins/docker
+  settings:
+    repo: madeorsk/clang-llvm-meson-buildtools
+    tags: ${DRONE_TAG}
+    username:
+      from_secret: docker_registry_username
+    password:
+      from_secret: docker_registry_password
+  when:
+    ref:
+      - refs/tags/*