Introduce tenup-content-connect-update-relationships-order action

[s3rgiosan]

Description of the Change

Introduces a new tenup-content-connect-update-relationships-order action so extenders can run logic after relationship order is saved. It fires from PostToPost::save_sort_data() and both PostToUser sort methods, covering all three directions — post-to-post, post-to-user, and user-to-post — and passes the object ID, the ordered IDs, the relationship name, and the relationship type.

This is a rebase of #115 (@ocean90) onto the 2.0.0 line. Changes vs. the original PR:

• Resolved a trivial whitespace/alignment conflict against develop (kept develop's formatting).
• Bumped the docblock @since from 1.7.0 to 2.0.0 (1.7.0 never shipped).
• Corrected the @param docs on the canonical block: $object_id also carries a user ID in the user-to-post fire, so the description is now type-agnostic.

Original authorship is preserved (Author: Dominik Schilling, plus a Co-authored-by trailer).

Closes #114

How to test the Change

1. Register a post-to-post and a post-to-user relationship with sortable order enabled.
2. Hook the new action:

   add_action(
       'tenup-content-connect-update-relationships-order',
       function ( $object_id, $ordered_ids, $name, $type ) {
           error_log( "order updated: {$type} / {$name} / {$object_id} => " . implode( ',', $ordered_ids ) );
       },
       10,
       4
   );

3. Reorder related items on a post edit screen (post-to-post and post-to-user) and save.
4. Confirm the action fires once per save with the correct $type (post-to-post, post-to-user) and the ordered IDs matching the UI.
5. For user-to-post, trigger PostToUser::save_user_to_post_order() (API level) and confirm $object_id is the user ID and $type is user-to-post.

Changelog Entry

Added - tenup-content-connect-update-relationships-order action for developers.

Credits

Props @ocean90

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.