fix an issue with siteid path parameters

In trying to re-use the model of the siteid, which is marked
read-only, it became known that marking a path parameter as read-only
causes the generated code to ignore the values passed, resulting in
400 bad request errors.

So I've duplicated the model-based objectid schema to a property and
dropped the read-only property, so now all works as expected.

BACK-3632

Author: ewollesen

reference/clinic.v1.yaml

@@ -2664,7 +2664,7 @@ components:
       in: path
       required: true
       schema:
-        $ref: ./clinic/models/siteId.v1.yaml
+        $ref: ./common/parameters/objectId.v1.yaml
     userId:
       name: userId
       in: path

reference/common/parameters/objectId.v1.yaml

@@ -0,0 +1,6 @@
+title: Object Id
+type: string
+description: String representation of a resource id
+minLength: 24
+maxLength: 24
+pattern: '^[a-f0-9]{24}$'