Kiln mev boost (#3062)

## Issue Addressed

MEV boost compatibility

## Proposed Changes

See #2987

## Additional Info

This is blocked on the stabilization of a couple specs, [here](https://github.com/ethereum/beacon-APIs/pull/194) and [here](https://github.com/flashbots/mev-boost/pull/20).

Additional TODO's and outstanding questions

- [ ] MEV boost JWT Auth
- [ ] Will `builder_proposeBlindedBlock` return the revealed payload for the BN to propogate
- [ ] Should we remove `private-tx-proposals` flag and communicate BN <> VC with blinded blocks by default once these endpoints enter the beacon-API's repo? This simplifies merge transition logic. 

Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: realbigsean <sean@sigmaprime.io>

beacon_node/beacon_chain/Cargo.toml

@@ -59,7 +59,7 @@ strum = { version = "0.21.0", features = ["derive"] }
 logging = { path = "../../common/logging" }
 execution_layer = { path = "../execution_layer" }
 sensitive_url = { path = "../../common/sensitive_url" }
-superstruct = "0.4.0"
+superstruct = "0.4.1"
 
 [[test]]
 name = "beacon_chain_tests"