Scope shouldOverrideBuilder flag for Cancun (ethereum#425)

* Include shouldOverrideBuilder to Cancun scope

* Cosmetic fix

Author: mkalinin

src/engine/cancun.md

@@ -146,6 +146,7 @@ and proofs corresponding to the `versioned_hashes` included in the blob transact
   - `executionPayload`: [`ExecutionPayloadV3`](#ExecutionPayloadV3)
   - `blockValue` : `QUANTITY`, 256 Bits - The expected value to be received by the `feeRecipient` in wei
   - `blobsBundle`: [`BlobsBundleV1`](#BlobsBundleV1) - Bundle with data corresponding to blob transactions included into `executionPayload`
+  - `shouldOverrideBuilder` : `BOOLEAN` - Suggestion from the execution layer to use this `executionPayload` instead of an externally provided one
 * error: code and message set in case an exception happens while getting the payload.
 
 #### Specification
@@ -161,6 +162,8 @@ Refer to the specification for [`engine_getPayloadV2`](./shanghai.md#engine_getp
 
 4. Client software **MUST** return `-38005: Unsupported fork` error if the `timestamp` of the built payload is less than the Cancun activation timestamp.
 
+5. Client software **MAY** use any heuristics to decide whether to set `shouldOverrideBuilder` flag or not. If client software does not implement any heuristic this flag **SHOULD** be set to `false`.
+
 ### Deprecate `engine_exchangeTransitionConfigurationV1`
 
 This document introduces deprecation of [`engine_exchangeTransitionConfigurationV1`](./paris.md#engine_exchangetransitionconfigurationv1). The deprecation is specified as follows:

src/engine/openrpc/methods/payload.yaml

@@ -124,6 +124,7 @@
         - executionPayload
         - blockValue
         - blobsBundle
+        - shouldOverrideBuilder
       properties:
         executionPayload:
           title: Execution payload
@@ -134,6 +135,9 @@
         blobsBundle:
           title: Blobs bundle
           $ref: '#/components/schemas/BlobsBundleV1'
+        shouldOverrideBuilder:
+          title: Should override builder flag
+          type: boolean
   errors:
     - code: -38001
       message: Unknown payload