feat: finality gadget server

[parketh]

Summary

This PR implements the finality gadget server, a stateful program used to track consecutive quorum and query the latest BTC-finalized block.

Integration tests are seperately added in the finality-provider repo (see below)

• feature overview: https://github.com/babylonlabs-io/pm-integration/issues/14
• integration tests: test: op e2e finality gadget daemon itest finality-provider#26

Test plan

To run tests:

make test

To run the finality gadget daemon:

make install
opfgd start --cfg config.toml

Note that running the daemon with the default configs will throw a block %d be finalized according to client but is not error, because there aren't any FPs signing blocks, i.e. blocks are not registered as finalized. For testing purposes, we can override queryIsBlockBabylonFinalized in finalitygadget.go to return true, nil for now.

one the daemon is running, we can use Postman to test gRPC (need to import the finalitygadget.proto file) with localhost:8080 as the URL:

then you can invoke queries like:

[SebastianElvis]

That's a lot. Great work!

[bap2pecs]

love this PR! great work

[parketh]

thanks for latest round of comments @SebastianElvis @bap2pecs, have addressed these

[bap2pecs]

thanks for the changes! look great. feel free to ship the code