feat: Ability to remove inbox avatar (#2885)

* Delete inbox avatar

1) New API endpoint added for deleting inbox avatar.
2) Delete avatar button in the inbox settings page.

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/dashboard/api/inboxes.js

@@ -13,6 +13,10 @@ class Inboxes extends ApiClient {
   getCampaigns(inboxId) {
     return axios.get(`${this.url}/${inboxId}/campaigns`);
   }
+
+  deleteInboxAvatar(inboxId) {
+    return axios.delete(`${this.url}/${inboxId}/avatar`);
+  }
 }
 
 export default new Inboxes();