Improve playbook runner speed

[adityathebe]

At the moment, runners poll for playbook actions @every 1m. Once it runs it, the result is then pushed @every 15s.

Due to this, it takes at few minutes to complete a simple playbook with one action.
With more actions, time to complete increases linearly.

Proposed solutions

1. Long polling

Runners shouldn't run on a schedule. Rather they should be continuously polling for actions in a never ending for loop.

2. Stateful connection

Somehow maintain a stateful TCP connection between the upstream and the runner.
Runners "subscribe" to upstream on startup and upstream "publishes" to the connection whenever a new action for that agent is inserted to db.

[moshloop]

Implement HTTP/2 long polling for maximum portability + channels to incrementally push playbook action / artifacts /