Expose more builder_boost_factor settings in VC

[michaelsproul]

Description

In #4813 we are adding the --produce-block-v3 flag for using the v3 block production APIs in the VC. We are supporting the existing builder_proposals: bool config for backwards compatibility, by translating builder_proposals: false to builder_boost_factor=0.

As described by @eserilev here (#4813 (comment)) it would be good to have some more expressive options in the VC like:

• prefer_builder_proposals: bool: shorthand for builder_boost_factor=u64::MAX
• builder_boost_factor: u64: support for other values configured on a per-validator basis

I don't think we necessarily need --local-always as this is what I was forced to translate builder_proposals: false to. If we deprecate builder_proposals then the "local always"/"prefer local" naming may be clearer.

[eserilev]

I'd like to pick this up

[michaelsproul]

Thanks Eitan, it's all yours!

[paulhauner]

Heyo, we're lining up for a v4.6.0 release by Tuesday (23rd Jan) driven by the need to include the Deneb upgrades for Sepolia and Holesky.

One of the blockers on this release is reinstating --always-prefer-builder-payload. Our RocketPool friends rely on this flag, it's critical to them.

@eserilev, I appreciate this is a tight timeframe so we're happy to get this sorted internally if you don't have the time for this. We'd ideally need to have something ready for testing this week or Monday. No pressure from our end, just let us know 🙏

[eserilev]

@paulhauner i should have something ready for review in a few hours!

[jimmygchen]

Completed in #5086