Protobufs for the relay

Why are these changes needed?

This PR adds protobufs for the relay. WIP.

[ ] I've made sure the lint is passing in this PR.
[ ] I've made sure the tests are passing. Note that there might be a few flaky tests, in that case, please comment that they are not relevant.
[ ] I've checked the new test coverage and the coverage percentage didn't drop.
Testing Strategy
- [ ] Unit tests
- [ ] Integration tests
- [ ] This PR is not tested :(