Allow GPs to click through to the agreement

We want GPs to be able to accept the agreement online. But at the moment
they don’t get automatically assigned to organisations. So we need to
let them enter the agreement accepting journey even if they don’t have
an organisation set up.

app/models/service.py

@@ -591,6 +591,13 @@ class Service(JSONModel):
     def get_api_key(self, id):
         return self._get_by_id(self.api_keys, id)
 
+    @property
+    def able_to_accept_agreement(self):
+        return (
+            self.organisation.agreement_signed is not None
+            or self.organisation_type == 'nhs_gp'
+        )
+
     @property
     def request_to_go_live_tags(self):
         return list(self._get_request_to_go_live_tags())