EIP-7840 : Add blob schedule to EL config files

Why this EIP neeeded?

• Currently, when the eth_feeHistory RPC method is called to fetch recent gas fee data, the EL queries the CL using the engine APIsengine_newPayloadV3 call to retrieve blobGasUsed and excessBlobGas. This creates unnecessary overhead, which this EIP aims to eliminate by providing a configuration-based solution.
• The aim is to enable dynamic adjustment of target and max blob counts per block, along with the blob base fee update fraction, while reducing complex handshakes over the Engine API.

EIP Proposal and Functioning

• Extend the configuration files with a new object blobSchedule which has following shape :

  "blobSchedule": {
  "cancun": {
    "target": 3,
    "max": 6,
    "baseFeeUpdateFraction": 3338477
  },
  "prague": {
    "target": 6,
    "max": 9,
    "baseFeeUpdateFraction": 5007716
  }
  }
  

  Implementation Considerations

• Clients must configure these settings for each fork, and if any are missing or incomplete, it is up to the client developers to determine how to handle the situation.

Risks & Mitigations

Risks

1. Improper handling of implementation may result in invalid block proposals.

Mitigations

1. Implement a fallback mechanism for blob configuration settings by either ensuring the config is set, defaulting max and target values to zero, or using values from the previous fork.