feat(mkdocs_build): always build on git tag

this allows the built files to always be available under the
latest tag job for downloading by the parent site.

!41

mkdocs/.gitlab-ci.yml

@@ -46,6 +46,14 @@
     - if: '$JOB_STOP_MKDOCS_BUILD'
       when: never
 
+      # Build docs on tag so they can be downloaded from the tag job and are always available.
+    - if:  # condition_git_tag
+        $CI_COMMIT_TAG != null &&
+        $CI_COMMIT_BRANCH == null
+      exists:
+        - '{docs/**,pages/**}/*.md'
+      when: always
+
     - if:  # condition_master_branch_push
         $CI_COMMIT_BRANCH == "master" && 
         $CI_PIPELINE_SOURCE == "push"