[FR] Per validator fee recipient

[kanewallmann]

It is highly desirable for Rocket Pool (and likely other staking providers) that the feeRecipient on execution payloads be configurable on a per validator account basis.

In the case of Rocket Pool, users may be running both solo validators where they are entitled to the full reward and Rocket Pool validators where only a portion of the rewards belongs to them. Not having this feature would exclude Nimbus as a possible client for users running this setup.

Depending on our chosen implementation of priority fee processing, we may even require this feature for all Rocket Pool node operators as we may need to account for priority fees on an individual validator basis. In this situation, this feature would be critical for our interoperability with Nimbus.

A simple mapping of validator indices to fee recipients would be sufficient for our use case.

I can imagine that this flexibility would be desirable in other advanced use cases as well.

[tersec]

For reference, how Teku does this: Consensys/teku#4894

[zah]

The support for specifying per-validator fee recipient was implemented in #3652

The issue will be closed after we document the configuration steps in the Nimbus guide (#3723). In the first iteration, the user will have to manually create configuration files, while in the future we will also support a command-line interface for this (#3723 and #3725)

[arnetheduck]

We should also support the more simple and stateless --suggested-fee-recipient option for this - ie it's messy to have to create a file or use the keymanager api for simple use cases

Edit: Oops, we already do :)