Tracking: update constraints-API in PBS

[mempirate]

Context

This issue tracks the implementation of the new constraints API across the PBS pipeline. Note that we can implement Blob Express Lane in the relay & builder.

Bolt Sidecar

Beta Give feedback

1. Update constraints-API client #208
   C: bolt-sidecar T: feature +2
   
2. Holesky testing & launch instructions #225
   +0
   
3. Update constraints-API to use pubkey instead of index #230
   4 of 5
   T: tracking +1
   
4. feat(sidecar): Create a delegations file format and load it on startup #290
   C: bolt-sidecar T: feature +2
   
5. Support per-validator signer #283
   C: bolt-sidecar T: chore +2
   

@merklefruit can work on this:

Flashbots Builder

Beta Give feedback

1. Update types
2. Remove authentication header (not needed according to the relays)
3. Update constraints stream (new format & types)
4. Nit: get rid of "preconf" wording everywhere, change to constraints
5. Remove Bolt demo events
6. Add relevant log lines

@namn-grg is working on this:

Helix

Beta Give feedback

1. Implement proposer-facing constraints-API
2. Implement builder-facing constraints-API
3. Verify BLS signatures on SignedConstraints (will be signed with commit-boost signing domain!)
4. Verify authorized BLS pubkey on SignedConstraints!