Allow passing request/view context to JWT token generation

[AbhijithKonnayil]

Fixes : #720

Currently, dj-rest-auth provides the user object to the JWT serializer, but there is no straightforward way to inject custom claims that depend on the request context (e.g., origin, device ID, user-agent) or view-specific logic.

This PR introduces a flexible mechanism to pass such context into the token generation process.

Changes

• Serializers: Added TokenWithCustomClaimsSerializer which supports dynamic injection of extra claims.
• Views: Added a hook get_non_user_custom_claims(request) in LoginView. Subclasses can override this to return a dictionary of claims derived from the request.
• Utilities: Updated jwt_encode to accept and propagate custom_claims.
• Settings: Updated default JWT_TOKEN_CLAIMS_SERIALIZER to the new custom claims serializer to support this feature out-of-the-box.

class MyLoginView(LoginView):
    def get_non_user_custom_claims(self, request, *args, **kwargs):
        return {
            'organization_id': request.data.get('org_id'),
            'ip_address': self.request.META.get('REMOTE_ADDR')
        }