[builder API] Enable Web3Signer tests for validator registration

[realbigsean]

Description

We currently run tests against the Consensys web3 signer. We have tests in #3194 that are commented out until the functionality for validator registration signatures are implemented.
This is the relevant Consensys issue.

[siladu]

Hi @realbigsean web3signer validator registration support is available on master now.
If you use docker it's on the develop tag: docker pull consensys/web3signer:develop

We're expecting to release web3signer 22.7.0 this week or next with this in.

The shape of the signing request is documented here under the VALIDATOR_REGISTRATION type: https://consensys.github.io/web3signer/web3signer-eth2.html#tag/Signing

[realbigsean]

Thanks @siladu !

[siladu]

Hi again @realbigsean this has now been released: https://github.com/ConsenSys/web3signer/releases/tag/22.7.0

Note, since my last message, the request format has changed: we no longer require an epoch to be sent.

[realbigsean]

Completed in 7aa2a74