stacks-blockchain-api : Add support for S&P event streams

[rafaelcr]

We should add the option to receive Stacks node events via S&P (Redis) so we can move to that configuration in our deployments, while keeping the Stacks node event server fully maintained.

This will allow us to have more flexibility for replays and/or disaster recovery.

[saralab]

In May, our focus will be to add integration tests to S&P before we integrate the stacks-blockchain-api.