Identifier for builder to proposer transaction

**Current Understanding**
- The Builder will set their own feeRecipient for a block
- They will then send a share of their earnings to the proposer (to their specified "feeRecipient" account in a transaction

**The Problem**
For a staking provider with multiple customers, it is difficult to:
a) Prove to customers they have received the agreed upon earning.
b) Know how much to charge customers (if fees are based on a percentage of rewards)

Some kind of indicator or marker on the transaction would be great 🙏

# Update

Continuation of the discussion here: https://collective.flashbots.net/t/block-scoring-for-mev-boost-relays/202