Helix's get constraints API does not response constraints with related preconfer pubkey

[Akagi201]

Note that: preconfer pubkey may be not needed. Because when the validator is selected to propose a block, all the constraints should be its delegated preconfer if there is no errors.

Now the /constraints/v1/constraint/{slot} API only return a tx array constraint.

{
  "slot": 0,
  "constraints": [
    [
      {
        "tx": "string"
      }
    ]
  ]
}

We need to add preconfer pubkey field

{
  "slot": 0,
  "constraints": [
    [
      {
        "preconfer_pubkey": "string"
        "tx": "string"
      }
    ]
  ]
}

The preconfer pubkey is useful for rbuilder and taiyi-boost local builder to distinguish the constraints, for example, local builder can do a filtering, only include its own configured preconfer's constraints.

Similiarly, Bolt has pubkey field: https://docs.boltprotocol.xyz/technical-docs/api/relay#constraints