Add 'maybe_add_phabricator_link' to fxsync new and existing prod config (#1214)

* Update config.prod.yaml

Added `- sync_keywords_labels` to fxsync's "existing" steps.

* Add maybe_add_phabricator_link to config for sync

Added 'maybe_add_phabricator_link' to existing and new states for fxsync.

Author: ddurst

config/config.prod.yaml

@@ -212,12 +212,14 @@
         - maybe_assign_jira_user
         - maybe_delete_duplicate
         - maybe_update_issue_status
+        - maybe_add_phabricator_link
       existing:
         - update_issue_summary
         - maybe_assign_jira_user
         - maybe_update_issue_status
         - sync_whiteboard_labels
         - sync_keywords_labels
+        - maybe_add_phabricator_link
       comment:
         - create_comment
     status_map: