Reproducible build (tracking issue)

[Davidson-Souza]

Reproducible builds are a very useful security primitive, as they reduce the risk of supply chain attack and single point of failure on binary redistribution.

This issue tacks the progress towards making floresta builds deterministic. This should allow the community to verify our binaries. It should be updated as the project goes to reflect our current plans and tasks.

• Automate the nix-based build
• Figure out how to cross build for Windows
• Create a repo for attestation, like bitcoin core's