Chore: Inbox Members API improvements (#3008)

- New Inbox Member APIs
- Return JSON errors for Platform APIs

swagger/parameters/inbox_id.yml

@@ -0,0 +1,6 @@
+in: path
+name: inbox_id
+schema:
+  type: integer
+required: true
+description: The ID of the Inbox

swagger/parameters/index.yml

@@ -7,6 +7,9 @@ agent_bot_id:
 team_id:
   $ref: ./team_id.yml
 
+inbox_id:
+  $ref: ./inbox_id.yml
+
 hook_id:
   $ref: ./hook_id.yml