[RBAC] Add field to permission model to capture the service identifier

[AlanCoding]

Part of the reason for introducing the DABPermission model was to do this work. This proposes to add a new field to that model which has a similar format as ResourceType.name. As the resource type name field is of format "{service}.{model}", this new field would be of format "{service}.{action}_{model}".

This would be an informative field for use by API clients. It will be logically commutable from the other fields and the resource registry. This has to be saved in the migration logic.

Tentatively, say this field is named full_name. Because name is taken.

The serializer for /api/v1/role_definitions/ will then use a SlugRelatedField with many=True and slug_field="full_name". This means that PermissionField will be deleted.

That will take "choices" away from the OPTIONS data, which implies/obligates us to add a new endpoint to provide options for permissions. The API design constraints related to that are complex, and is one thing that has prevented me from getting this done before now.

[AlanCoding]

Saying this is an "enhancement" because it should allow query param filtering like /api/v1/role_definitions/?permissions__full_name=shared.view_organization