Chore: API Improvements (#2956)

- API to fetch info of a single inbox
- Document passing custom_attributes in the API
- Ability to filter contacts with contact identifier in search API

swagger/paths/inboxes/update.yml

@@ -5,6 +5,7 @@ patch:
   summary: Update Inbox
   description: Add avatar and disable auto assignment for an inbox
   parameters:
+    - $ref: '#/parameters/account_id'
     - name: id
       in: path
       type: number