add DVLA organisations to API

when services are created, they'll have a dvla_org_id of 001, or
HM Government. That can be changed later using a regular update call

app/models.py

@@ -113,6 +113,16 @@ class Organisation(db.Model):
     name = db.Column(db.String(255), nullable=True)
 
 
+DVLA_ORG_HM_GOVERNMENT = '001'
+DVLA_ORG_LAND_REGISTRY = '500'
+
+
+class DVLAOrganisation(db.Model):
+    __tablename__ = 'dvla_organisation'
+    id = db.Column(db.String, primary_key=True)
+    name = db.Column(db.String(255), nullable=True)
+
+
 class Service(db.Model, Versioned):
     __tablename__ = 'services'
 
@@ -147,6 +157,14 @@ class Service(db.Model, Versioned):
     sms_sender = db.Column(db.String(11), nullable=True)
     organisation_id = db.Column(UUID(as_uuid=True), db.ForeignKey('organisation.id'), index=True, nullable=True)
     organisation = db.relationship('Organisation')
+    dvla_organisation_id = db.Column(
+        db.String,
+        db.ForeignKey('dvla_organisation.id'),
+        index=True,
+        nullable=False,
+        default=DVLA_ORG_HM_GOVERNMENT
+    )
+    dvla_organisation = db.relationship('DVLAOrganisation')
     branding = db.Column(
         db.String(255),
         db.ForeignKey('branding_type.name'),

app/schemas.py

@@ -177,6 +177,7 @@ class ServiceSchema(BaseSchema):
     created_by = field_for(models.Service, 'created_by', required=True)
     organisation = field_for(models.Service, 'organisation')
     branding = field_for(models.Service, 'branding')
+    dvla_organisation = field_for(models.Service, 'dvla_organisation')
 
     class Meta:
         model = models.Service