[FEATURE REQUEST] Google Chat handler

[jhenderson-pro]

As a Sensu operator using Google Chat, I'd like to have an event handler to send alerts via the Google Chat API. See:

https://developers.google.com/chat/api/reference/rest
https://chat.googleapis.com/v1/spaces/

[fguimond]

@fguimond to provide instructions on how to create a Sensu plugin.

Additionally you can look at https://github.com/sensu/sensu-microsoft-teams-handler for the arguments necessary for this plugin. We might modify them a little bit based on API constraints but the general structure should be very similar.