add flashbots (milestone 1) consensus beacon block types (#3314)

* add flashbots (milestone 1) consensus beacon block types

* remove MEV types from main bellatrix spec module

beacon_chain/spec/datatypes/bellatrix.nim

@@ -326,14 +326,14 @@ type
 
   SomeSomeSignedBeaconBlock* = SomeSignedBeaconBlock | altair.SomeSignedBeaconBlock | phase0.SomeSignedBeaconBlock
 
-  BlockParams* = object
+  BlockParams = object
     parentHash*: string
     timestamp*: string
 
-  BoolReturnValidRPC* = object
+  BoolReturnValidRPC = object
     valid*: bool
 
-  BoolReturnSuccessRPC* = object
+  BoolReturnSuccessRPC = object
     success*: bool
 
 func encodeQuantityHex*(x: auto): string =

beacon_chain/spec/datatypes/bellatrix_mev.nim

@@ -0,0 +1,39 @@
+# beacon_chain
+# Copyright (c) 2022 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+import "."/[altair, bellatrix]
+
+type
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#blindedbeaconblockbody
+  # This is forked from bellatrix.BeaconBlockBody with execution_payload
+  # replaced with execution_payload_header
+  BlindedBeaconBlockBody = object
+    randao_reveal*: ValidatorSig
+    eth1_data*: Eth1Data
+    graffiti*: GraffitiBytes
+    proposer_slashings*: List[ProposerSlashing, Limit MAX_PROPOSER_SLASHINGS]
+    attester_slashings*: List[AttesterSlashing, Limit MAX_ATTESTER_SLASHINGS]
+    attestations*: List[Attestation, Limit MAX_ATTESTATIONS]
+    deposits*: List[Deposit, Limit MAX_DEPOSITS]
+    voluntary_exits*: List[SignedVoluntaryExit, Limit MAX_VOLUNTARY_EXITS]
+    sync_aggregate*: SyncAggregate
+    execution_payload_header*: ExecutionPayloadHeader
+
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#blindedbeaconblock
+  # This is forked from bellatrix.BeaconBlock with body replaced with
+  # BlindedBeaconBlockBody
+  BlindedBeaconBlock = object
+    slot*: Slot
+    proposer_index*: uint64
+    parent_root*: Eth2Digest
+    state_root*: Eth2Digest
+    body*: BlindedBeaconBlockBody
+
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#signedblindedbeaconblock
+  SignedBlindedBeaconBlock = object
+    message*: BlindedBeaconBlock
+    signature*: ValidatorSig