* inbox: add GET public inbox key && POST inbox items endpoint
* inbox: update SyncItem to support inbox items
* inbox: update post inbox items request payload
* inbox: update post inbox item endpoint
* feat: get, add, & delete user's inbox api tokens
* inbox: generate inbox api key on the server
* inbox: use nanoid to generate api key && set created date on server
* inbox: set api key in constructor && increase default expiry date to 1 year