Add Debug Forkchoice endpoint support

[samcm]

Adds support for the new ForkChoice debug endpoint.

I wasn't entirely sure on the structure/formatting of where to place these structs. Happy to be advised if there is a better way to do things 🙏

Thank you!

[mcdee]

This endpoint doesn't seem to be very well supported:

• lighthouse: no support
• nimbus: returns data format not as per the spec
• prysm: no support
• teku: support

so 1/4 of the nodes on which I tried it. I'm a little concerned about adding support for this in to the codebase and then being pinged on issues using it due to the lack of downstream support. Are there plans for the various clients to add/fix support?

[samcm]

Yeah that's one of my concerns as well. Maybe it makes sense to rename the func to DebugForkChoice or something. As for support, yeah it's in flight with multiple clients:

Teku: Implemented
Lighthouse: Open PR sigp/lighthouse#4003
Prysm: In develop - prysmaticlabs/prysm@3d0ecdf
Nimbus: Behind --debug-fork-choice (I haven't validated the data though, you could definitely be correct that the format isn't per the spec)
Lodestar: Unfinalized implementation running on /eth/v0/debug/forkchoice

[samcm]

Happy for this to stay unmerged until more support lands in client releases @mcdee FWIW 🙏

[mcdee]

Yeah let's hold this until we see better coverage of support and can take a view on where it fits.

[samcm]

@mcdee All clients excluding Lodestar have support in at least their develop branches now 🙏

[mcdee]

One change required. Also, please could you add this call to the sleepy and erroring clients in the testclients directory? Thanks.

[mcdee]

There are a few errors being thrown up by the testing, please could you rebase this against he latest master and we'll see what needs to be addressed? Thanks.

[mcdee]

Not sure exactly where those errors are (the output of the testing looks bad), I'll merge this and fix if required in a separate commit.

[samcm]

Cheers @mcdee! Sorry I've been on holidays for a little bit, thank you for sorting that 🙏