Change logging for custom field deletion clean-up task

[briddo]

In addition to the work already done for #1582 on this PR, we need to add change logging for each updated object in nautobot.extras.tasks.delete_custom_field_data code here

[glennmatthews]

I think more generally this is a gap for all of our custom field background updates (such as populating default values for a newly created custom field).

[glennmatthews]

I think a "complete" fix here would involve all of the following background task functions in nautobot.extras.tasks:

• update_custom_field_choice_data should create ObjectChange records for each model instance impacted when changing the definition of a custom field choice.
• delete_custom_field_data should create ObjectChange records for each model instance impacted when deleting a custom field (or simply removing its association from a previously assigned content-type(s))
• provision_field should create ObjectChange records for each model instance impacted when adding a new custom field with a default value (or expanding the scope of such an existing custom field to a new content-type(s)).

For all of the above, if no data is changed on a given model instance, an ObjectChange should not be generated for that specific instance.

[gsnider2195]

This is going to require some more effort than initially estimated.

• Need to store the current user in something like thread local storage or contextvars so that m2m_changed signal and model save/delete methods can retrieve the user for change logging
• Need to be able to pass the user to celery tasks so that the worker knows which user to attach to the ObjectChange. Probably a good idea to add this to the celery request object and use this in a custom nautobot task class similar to the work in [WIP] Implementation of singleton pattern for Jobs #1081

[gsnider2195]

Some of this work was completed but depends on the change logging improvements in #2236 in order to log changes by the user responsible for triggering the background task.

2231.patch.txt

[lampwins]

Probably just need to convert these custom celery tasks to system jobs.

[lampwins]

Need to account for users in the ORM case.

[gsnider2195]

It probably doesn't make sense to make this a system job yet since we still don't support running jobs without a user (the ORM case here). We should be able to introspect nautobot.extras.signals.change_context_state to get the current user and pass it to the background task for the change logging.

[lampwins]

Always attempt to the user by whatever means are available (change context for example). As a last resort, allow system jobs to run without a user.