[bug] `FilterSerializerByOrganization` filters fields without organization

[pandafy]

FilterSerializerByOrganization filters queryset of all related fields using the organization_lookup. But, it might be possible that a model does not have relation to Organization (not even an indirect one, e.g. WiFiClient in openwisp-monitoring).

We should allow to exclude fields from the organization filtering.

[nemesifier]

@Aryamanz29 do you think this was fixed by 670ec93 ?

[Aryamanz29]

@Aryamanz29 do you think this was fixed by 670ec93 ?

@nemesifier I don't think this issue has been addressed, and I believe it remained unresolved during the development of multitenant capabilities for the Django Filters feature. This happened because we decided to complete that PR only for the Wi-Fi session REST API. Previously, we were also working on adding a REST API for Wi-Fi clients, and it was during that time that we encountered this bug.

[BelpHegoR17]

The issue occurred because FilterSerializerByOrganization was applying organization filtering to every related field, even when the related model had no connection to Organization. This caused fields from models like WiFiClient (which are not organization-based) to get incorrectly filtered.

My solution was to update the filter logic so that:

Before filtering a field, we check whether the field’s model actually has any relation to Organization.

We do this by dynamically scanning the model’s fields and only applying the filter if at least one relation to Organization exists.

If a model has no organization-related fields, its queryset is left untouched.

Existing behavior for direct Organization fields and include_shared is preserved.

This ensures that only models that truly belong to an organization get filtered, and all unrelated fields remain unaffected.