Forward validator registrations without decoding

[jtraglia]

📝 Summary

• Move functionality to new register_validator.go file.
• Forward validator registrations to each relay without decoding the message.
  • If the node sends validator registrations in SSZ, we inherit that.
• Add a wrapUserAgent method.

✅ I have run these commands

• make lint
• make test-race
• go mod tidy

[ralexstokes]

the code generally looks good. some notes:

• there are no tests for this AFACIT, we should test somehow before putting into a release
• there is a change in behavior here where mev-boost no longer verifies the validator registrations deserialize correctly; it should be fine (the relay will still do this, etc) but is somewhat of a notable change
• im not going all of the go APIs with a fine-toothed comb, so could be missing something with error handling, request processing, etc

[jtraglia]

there are no tests for this AFACIT, we should test somehow before putting into a release

Agreed. I've pushed some basic tests to ensure the forwarding works as expected.

there is a change in behavior here where mev-boost no longer verifies the validator registrations deserialize correctly; it should be fine (the relay will still do this, etc) but is somewhat of a notable change

Also agreed. But I feel that this is fine. The builder/relay should check this. Keep in mind it's possible for clients to connect directly to a single builder/relay and skip the mev-boost middleman. Meaning they need to handle bad inputs too.

[metachris]

nice code and docs/comments!