build: Creating a missing workflow file `add-remove-label-on-comment.yml`.

The .github/workflows/add-remove-label-on-comment.yml workflow is missing or needs an update to stay in
sync with the current standard for this workflow as defined in the
`.github` repo of the `openedx` GitHub org.

.github/workflows/add-remove-label-on-comment.yml

+# This workflow runs when a comment is made on the ticket
+# If the comment starts with "label: " it tries to apply
+# the label indicated in rest of comment.
+# If the comment starts with "remove label: ", it tries
+# to remove the indicated label.
+# Note: Labels are allowed to have spaces and this script does
+# not parse spaces (as often a space is legitimate), so the command
+# "label: really long lots of words label" will apply the
+# label "really long lots of words label"
+
+name: Allows for the adding and removing of labels via comment
+
+on:
+  issue_comment:
+    types: [created]
+
+jobs:
+  add_remove_labels:
+    uses: openedx/.github/.github/workflows/add-remove-label-on-comment.yml@master
+