feat: weather poller worker added

[linalim]

• Uses Agent to update args of field weather_published. When channel subscribed, the longitude-latitude pair is added to the list of states. When channel unsubscribed, it is removed.
• Implements Absinthe Socket Decorator and Absinthe Channel Decorator, which references code from: this link
• Currently, handle_in("unsubscribe") handles unsubscribing from all channels. Handling unsubscribing from each channel has not been implemented.
• To test out weather poller worker:
  • subscribe to weatherPublished using {longitude, latitude} pair in Graphiql
  • unsubscribe by exiting out of Graphiql

[cbarber]