Describe the bug
When attempting to update DNS resolver settings with pfblockerng installed an error gets thrown.

{
           "code" => 500,
         "status" => "internal server error",
    "response_id" => "FIELD_CHOICES_CALLABLE_NOT_FOUND",
        "message" => "Could not find choices callable method `get_python_script_options` in Field object nor its parent Model.",
           "data" => []
}

Python Script field is set to pfb_unbound which is the only option available when pfblockerng is installed.
I am assuming this is related to pfBlockerNG using a python script with the DNS resolver as when it is not installed this field is normally empty and unselectable.

To Reproduce
Pull settings JSON via GET /api/v2/services/dns_resolver/settings.
Set settings using same JSON, with or without changes, via PATCH /api/v2/services/dns_resolver/settings

Expected behavior
200 OK and new settings have been set.

pfSense Version & Package Version:

• pfSense Version: 2.7.2-RELEASE (Free Version)
• Package Version: v2.4.1

Affected Endpoints:

• URL: /api/v2/services/dns_resolver/settings