Fixes #18585: filtering circuits by location (#18641)

* Fixes #18585: filtering circuits by location

This also fixes a related issue where selected filter is not shown in
the filter form.

Changes:
- Adds `CircuitFilterSet.location_id` field to enable filtering with
  incoming GET params
- Adds `CirciotFilterForm.location_id` field to enable filtering from
  list form
- Adds `location_id` to the Location fieldset on `CircuitFilterForm`

* Adds test for new CircuitFilterset.location_id filter

netbox/circuits/filtersets.py

@@ -234,6 +234,11 @@ class CircuitFilterSet(NetBoxModelFilterSet, TenancyFilterSet, ContactModelFilte
         to_field_name='slug',
         label=_('Site (slug)'),
     )
+    location_id = django_filters.ModelMultipleChoiceFilter(
+        field_name='terminations___location',
+        label=_('Location (ID)'),
+        queryset=Location.objects.all(),
+    )
     termination_a_id = django_filters.ModelMultipleChoiceFilter(
         queryset=CircuitTermination.objects.all(),
         label=_('Termination A (ID)'),