Implement 2 minutes beacon node sync with checkpoint state

[remyroy]

Is your feature request related to a problem? Please describe.
It can take a few hours to sync a Nimbus beacon node on mainnet or any of the testnet from scratch.

Describe the solution you'd like
It should take only 2 minutes to sync a Nimbus beacon node from scratch using a recent finalized checkpoint state.

Additional context
See this video by Adrian Sutton from the Teku development team. You can get more details on the related Teku documentation page.

[remyroy]

Looking at the command line flags, it seems like this might already be implemented, but I'm not sure how exactly you would use it:

     --weak-subjectivity-checkpoint  Weak subjectivity checkpoint in the format
                               block_root:epoch_number.
     --finalized-checkpoint-state  SSZ file specifying a recent finalized state.
     --finalized-checkpoint-block  SSZ file specifying a recent finalized block.

Maybe this need just a little more documentation with some examples.

[mratsim]

It's a feature that is still being worked on, hence we don't publicize it at the moment.

[arnetheduck]

In particular, there are unresolved spec issues before it can be implemented in a secure and sustainable way - see ethereum/consensus-specs#2131 - teku currently operates in a grey zone of the spec when it syncs the way it does.

[arnetheduck]

Another way to start up quickly is to simply copy the existing sqlite database - it's one file that's fairly easy to move around.

[arnetheduck]

https://notes.status.im/nimbus-eth2-checkpoint-sync# outlines a rough technical roadmap for this feature

[arnetheduck]

#3209

[arnetheduck]

Released in 1.7.0: https://nimbus.guide/trusted-node-sync.html