Add publish_draft_release.sh (#752)

* Add publish_draft_release.sh

This new CI script will generate a list of differences between
this tagged version and the previous tagged version (including
substrate changes), and create a draft release on Github. Once
this is done, the draft release will be posted in Matrix (the
channel is determined by a Gitlab CI environment variable).

* Add highlighting gav for draft release

polkadot/.gitlab-ci.yml

@@ -269,6 +269,20 @@ publish-s3-release:
 
 
 
+publish-draft-release:
+  stage:                           deploy
+  image:                           parity/tools:latest
+  only:
+    - tags
+    - /^v[0-9]+\.[0-9]+\.[0-9]+.*$/        # i.e. v1.0.1, v2.1.0rc1
+  script:
+    - ./scripts/gitlab/publish_draft_release.sh
+  interruptible:                   true
+  allow_failure:                   true
+
+
+
+
 
 .deploy-template:                  &deploy
   stage:                           deploy