Support for auditSync and auditDetach on Auditable custom Pivot class

[txdFrancesco]

Allow the use of auditSync and auditDetach on BelongsToMany relations where the pivot class is an Auditable class.

This is useful in cases where the relation model is itself a Laravel model and may be updated (and thus audited) indipendently from the related models, without requring dedicated code around every ->auditSync call on the related models.

[willpower232]

are you able to correct your spaces to match the rest of the code and add some tests for the functionality you've added?

[txdFrancesco]

For the spaces sure, for the tests I'll need to add a couple of models to reproduce.
Users -> GroupMembers (with 'role' column) -> Groups could be an example of my case. Let me know if you have a better/preferred example structure. I'll update when I'm done, thanks

[txdFrancesco]

I added some tests that cover sync, attach and detach with an Auditable custom Pivot class.
AuditAttach is not affected by my code change, I put in the test anyway for completeness. Let me know if it is better to remove it.

The other tests are failing without the code change and are passing now.

[willpower232]

some final spaces and maybe wake up github actions