Firehose on Beacon

This is the poller implementation to create Firehose blocks from Beacon chains. It enables both Firehose and Substreams on Beacon chains. It supports all current specs (Phase0, Altair, Bellatrix, Capella and Deneb). For the Deneb spec we embed blobs into the firehose blocks.

The block proto can be found here.

Note this is still work in progress and the block type might change, nor do we have extensive testing and data validation yet.