Release script: add release notes to the git notes

This is a first change to get rid of the release commit on release branch.
Doing so will 1/ allows for git workflow (git cherry-pick), 2/ allows to
use merge feature from git notes.

--
Change-Id: Id6a93f0dc70b9efe8ff705f1dd2a16489989f281
Reviewed-on: https://cr.bazel.build/7337
MOS_MIGRATED_REVID=139904935
diff --git a/scripts/release/common.sh b/scripts/release/common.sh
index 20925fe..e17cedc 100755
--- a/scripts/release/common.sh
+++ b/scripts/release/common.sh
@@ -49,6 +49,11 @@
   git notes --ref=release show "$@" 2>/dev/null | xargs echo || true
 }
 
+# Extract the release notes from the git notes
+function get_release_notes() {
+  git notes --ref=release-notes show "$@" 2>/dev/null || true
+}
+
 # Returns the info from the branch of the release. It is the current branch
 # but it errors out if the current branch is not a release branch. This
 # method returns the tag of the release and the number of the current