Add bid proofs to the builder bid response

Author: g11tech

types/bellatrix/bid.yaml

@@ -12,6 +12,12 @@ Bellatrix:
       pubkey:
         $ref: "../../beacon-apis/types/primitive.yaml#/Pubkey"
         description: "BLS public key of builder."
+      fee_recipient:
+        $ref: '../../beacon-apis/types/primitive.yaml#/ExecutionAddress'
+        description: "The address the bid is paid to"
+      proofs:
+        $ref: "../proof.yaml#/Proofs"
+        description: "Proofs of pre and post balances of the `fee_recipient` account"
 
   SignedBuilderBid:
     type: object

types/proof.yaml

@@ -0,0 +1,13 @@
+Proofs:
+  type: array
+  items:
+    allOf:
+      - $ref: '#/Proof'
+  maxItems: 2
+
+Proof:
+  type: array
+  items:
+    allOf:
+      - $ref: "../beacon-apis/types/primitive.yaml#/Bytes32"
+  maxItems: 32