Telemetry support

[AndreiEres]

We'd like to add some additional off-chain information from the telemetry. The telemetry itself is an event stream. There is no state, so we need to subscribe to it and save the current state in our storage. We can start with collecting existing events, but then we can also add support of additional events related to parachains work.

Progress

The work is expected to be large and can be tracked in the following tasks:

• Add telemetry backend support for dispute tracking #178
• Tool request: validator keys tracking #98
• Interface directly with polkadot node to collect gossip messages #91

[sandreim]

#91 is out of date, I'll update the ticket to current vision