make subtree "split" overhaul

In order to create cleaner histories we should be using subtree split
and push in order to preview the changes as an MR before pushing to
main.

.gitlab/README.md

@@ -0,0 +1,9 @@
+# Adding the "common" subtree as your .gitlab folder
+
+```bash
+# Add the subtree as a remote
+git subtree add --prefix .gitlab git@gitlab.ducoterra.net:services/common.git main --squash
+
+# Now you can run the following to update
+make make-update
+```