Update constraints-API to use pubkey instead of index

[mempirate]

Context

In the constraints-API we've used the validatorIndex to link validators to their signature. This works if the relay has a mapping from validatorIndex => pubkey, which not all of them do. So we should modify the constraints-API to use pubkey instead of validatorIndex in the following endpoints:

• submit_constraints
• delegate
• revoke

We should also update the API docs to reflect this: https://chainbound.github.io/bolt-docs/api/builder

Tasks

Beta Give feedback

1. Update submit_constraints
2. Update delegate
3. Update revoke
4. Update types across PBS stack
5. Update documentation

[namn-grg]

Changes in the builder can be done together in #209 when updating builder for the new constraint api (cc @merklefruit )