Builder api registration pubkey override for Distributed validators

[ciaranmcveigh5]

Description

For distributed validators to generate an aggregate signature the signed contents must be the same.

In the builder registration payload there is a pubkey field.

Each co-validator in a distributed validator has a pubkey-share which together form the aggregated pubkey that the network see's

The co-validators are currently putting their local key which is the pubkey-share into the validator registration - this means the registration contents don't match across the co-validators

The pubkey in the payload should be the aggregated pubkey - we can do this via a builder_registration_pubkey_override in the validator_defintions.yml

Present Behaviour

No way to override pubkey field in a builder registration

Expected Behaviour

Ability to specify pubkey override for each validator via validator_defintions.yml

Steps to resolve

In the process of raising a PR