Forward events through a websocket

[thclark]

Feature request

Use Case

We often need to consume events created by services in a frontend, which means that upon receipt in django they must be emitted through a websocket endpoint.

We may also need to view the event stream at a later date (e.g. long after the question has been asked and the channels cache has been flushed.

Proposed Solution

• Create a 'chatroom' consumer for a given question
• Authenticate connections to it using a token (available on the question model so we can pass the token to those we want to view the stream)
• On receipt of an event, emit it forward to connected clients
• On connection after the start of the question stream, all events since the start of the question should be flushed through to the newly connected client
• In the event of stale connections (i.e. connections made much later after the channel cache in REDIS is cleared) we'll need to re-flush events through the consumer (using the database as a source, instead of the original event stream) so clients always receive the full event stream.