refactor payload construction for awxkit

This fixes container_group creation to allow passing
"is_container_group" and "credential" to the "create" method
on instance groups, and refactors other page objects
to use a common utility function to eliminate copy-pasted code

awxkit/awxkit/utils/__init__.py

@@ -319,6 +319,23 @@ def update_payload(payload, fields, kwargs):
     return payload
 
 
+def set_payload_foreign_key_args(payload, fk_fields, kwargs):
+    if isinstance(fk_fields, str):
+        fk_fields = (fk_fields,)
+
+    for fk_field in fk_fields:
+        rel_obj = kwargs.get(fk_field)
+        if rel_obj is None:
+            continue
+        elif isinstance(rel_obj, int):
+            payload.update(**{fk_field: int(rel_obj)})
+        elif hasattr(rel_obj, 'id'):
+            payload.update(**{fk_field: rel_obj.id})
+        else:
+            raise AttributeError(f'Related field {fk_field} must be either integer of pkid or object')
+    return payload
+
+
 def to_str(obj):
     if isinstance(obj, bytes):
         return obj.decode('utf-8')