Chore: Document Conversation APIs in swagger (#552)

* Added the documentation for the conversation APIs - 8 endpoints
* Added descriptions for the existing endpoints
* Added new resource models and updated some parts of the contact API

swagger/definitions/resource/user.yml

@@ -0,0 +1,19 @@
+type: object
+properties:
+  id:
+    type: number
+  uid:
+    type: string
+  name:
+    type: string
+  email:
+    type: string
+  account_id:
+    type: number
+  role:
+    type: string
+    enum: ['agent', 'administrator']
+  confirmed:
+    type: boolean
+  nickname:
+    type: string