Migrate the API server from Express to Fastify

[rafaelcr]

[rafaelcr]

@zone117x and myself were discussing a plan for this issue.

The current idea is to gradually migrate our current endpoints from /extended/v1 on Express into /extended/v2 on Fastify. This will allow us to:

1. Continue supporting the current endpoints for a set amount of time we can define, with zero interruption and/or change risk to current users.
2. Redefine all response JSON schemas. Current schemas are brittle, very hard to maintain, and are not standardized across endpoints. This change will also provide schema and param validation for free and it will make schema documentation generation trivial.
3. Migrate routers slowly and roll them out as we go (block endpoints, tx endpoints, account endpoints, BNS, etc.)
4. Align new endpoint rollouts to upcoming Stacks launches such as sBTC and the Nakamoto release.

In the end, we can define a sunset date for /extended/v1 that works for all users and slowly encourage new players to move to /extended/v2.

cc @smcclellan