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/forms/filtersets.py

@@ -126,7 +126,7 @@ class CircuitFilterForm(TenancyFilterForm, ContactModelFilterForm, NetBoxModelFi
             'type_id', 'status', 'install_date', 'termination_date', 'commit_rate', 'distance', 'distance_unit',
             name=_('Attributes')
         ),
-        FieldSet('region_id', 'site_group_id', 'site_id', name=_('Location')),
+        FieldSet('region_id', 'site_group_id', 'site_id', 'location_id', name=_('Location')),
         FieldSet('tenant_group_id', 'tenant_id', name=_('Tenant')),
         FieldSet('contact', 'contact_role', 'contact_group', name=_('Contacts')),
     )
@@ -181,6 +181,11 @@ class CircuitFilterForm(TenancyFilterForm, ContactModelFilterForm, NetBoxModelFi
         },
         label=_('Site')
     )
+    location_id = DynamicModelMultipleChoiceField(
+        queryset=Location.objects.all(),
+        required=False,
+        label=_('Location')
+    )
     install_date = forms.DateField(
         label=_('Install date'),
         required=False,