Websocket support for Webhook Events + Actions

Alexis suggested I create an issue to track this.

Websocket support for events and actions would be fantastic. This improves performance and latency significantly, and reduces the amount of data sent over the wire.

I did some poking around and it looks like this bit is where the handler for Websocket requests would need to go for events:

https://github.com/hasura/graphql-engine/blob/27910004752e430dbe6c4607f4e3f50e6c198c02/server/src-lib/Hasura/Events/Lib.hs#L400-L429

I would love to learn a bit of Haskell by implementing this, but it may be the case that I do not have the time or could not learn quickly enough to do it in a timely manner.

Start by reading the referenced handler area in server/src-lib/Hasura/Events/Lib.hs at lines 400-429 to understand how event WebSocket requests would fit. Investigate how Webhook Events and Actions are currently handled, then define the WebSocket behavior and validate it with the relevant existing tests. Done means both event and action delivery support the proposed WebSocket path without regressions.

Written by the indexing model from the issue text.