Add support for multiple fee recipients

[tbenr]

PR Description

The PR introduces two new params for validator client:

• --Xvalidators-proposer-config: allows to specify a file path or a URL from which retrieve the configuration

• --Xvalidators-proposer-config-refresh-enabled: enables reload of the config every time VC is about to call prepare_beacon_proposer API (which currently happen at the beginning of each epoch)

the config is an extensible json file which allows to specify:

• a proposer configuration for multiple validator public key.
• a default proposer configuration for validator public keys not included in the previous mapping.

proposer configuration currently contains only fee_recipient. It can be extended to include other information (ie block builder URL)

behaviour details

• if --Xvalidators-proposer-config is specified, VC during initialisation will try to load the configuration. If fails (or the json config is invalid\incorrect) VC will fail start up
• if --Xvalidators-proposer-config-refresh-enabled is activated, if config reload fails, the last valid configuration will be used.

config json structure

{
  "proposer_config": {
    "0xa057816155ad77931185101128655c0191bd0214c201ca48ed887f6c4c6adf334070efcd75140eada5ac83a92506dd7a": {
      "fee_recipient": "0x50155530FCE8a85ec7055A5F8b2bE214B3DaeFd3",
    }
  },
  "default_config": {
    "fee_recipient": "0x6e35733c5af9B61374A128e6F85f553aF09ff89A"
  }
}

proposer_config is optional
default_config is mandatory
fee_recipient is mandatory in each config

How fee recipient will be actually chosen

• when --Xvalidators-proposer-config is used in VC

  • fee_recipient from a specific validator in the config
  • otherwise, fee_recipient from default_config in the config
  • otherwise, --Xvalidator-proposer-default-fee-recipient at beacon node

• when --Xvalidators-proposer-default-fee-recipient is used in VC

  • fee_recipient from --Xvalidators-proposer-default-fee-recipient in VC
  • otherwise, --Xvalidator-proposer-default-fee-recipient at beacon node

additional notes

currently, IO is blocking (file access as well as URL access). We have 5 threads on validator runner, to be evaluated if it is enough for the moment. It can be improved by migrating to async IO.

Fixed Issue(s)

fixes #4850

Documentation

• I thought about documentation and added the documentation label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[ajsutton]

I'm a bit out of it after staying up late so not sure I've properly understood this. Left a few comments but will have to come back to review it properly. Sorry.

[ajsutton]

Makes much more sense now I'm awake properly. Looks good generally, mostly just tweaks to how concurrency is handled.

[ajsutton]

LGTM. Given the OwnedValidators change turned out to be smaller than I expected feel free to pull that into here before merging as well.

[tbenr]

LGTM. Given the OwnedValidators change turned out to be smaller than I expected feel free to pull that into here before merging as well.

I improved it by managing potential not-yet-existing indices