Use autocompletion for user in TokenAdmin

[tchaumeny]

The user table does typically contain a large number of entries and the default select field in the admin can quickly become unusable.

I suggest to set autocomplete_fields = ("user",) here, or at least to make it configurable.

[tomchristie]

Will the admin automatically include the necessary search-autocomplete URL?
Do we need to be concerned that adding this would break some existing installations that are subclassing and using a custom formfield_override? https://docs.djangoproject.com/en/4.0/ref/contrib/admin/#django.contrib.admin.ModelAdmin.formfield_overrides

[tchaumeny]

To your first question I would answer yes as it is working on my project and I didn't have to configure anything.

I would suggest to make it optional with a default to the previous behavior so as to maintain backward-compatibility.

[tomchristie]

👉 #8534