♻️ Add minor refactor to file migrations

Relevant changes:

- Add the ability to create migration in both directions, defaulting
  to identity if not provided
- Move the version attribute to file table column for to make it more
  accessible (previously it was on data blob)
- Reduce db update operations on file-update rpc method

backend/src/app/srepl/helpers.clj

@@ -66,6 +66,7 @@
     (db/update! conn :file
                 {:revn (:revn file)
                  :data (:data file)
+                 :version (:version file)
                  :features (:features file)
                  :deleted-at (:deleted-at file)
                  :created-at (:created-at file)