Hardened broker reconnection strategies

Iterates on a more-aggressive reconnection strategy for dealing with with cases where connectivity with Cortex backend is lost.

Adds snyk-broker restarts on:

• Websocket tunnel close or interruption
• Idle timeout (default: 5m) with no traffic from backend

What's Changed

• Fix broker reconnection: channel-based restart with persistent watchdog by @shawnburke in #84

Full Changelog: v0.1.10...v0.2.0