refactor writer to move away from chainhooks

[rafaelcr]

Since we're discontinuing Chainhooks v1 and this is the only live service that still depends on it, we should refactor the writer to either:

• Consume Stacks node events directly from SNP
• Go back to reading the Stacks API DB directly (perhaps with a lighter polling algo)
• Add a secondary Redis queue that receives updates from Stacks API similar to Chainhooks v2

This will allow us to sunset Chainhooks v1 completely