Expose current sync committee and next sync committee per pubkey in the validator prometheus metrics

[ybstaked]

🚀 Feature Request

Description

Mainly need to know two things (from sync committee perspective):

• which pubkey is in a sync committee currently
• which pubkey will be in a sync committee next

If we're really concerned about data, then as a baseline, even just knowing that the validator has one of the keys in sync committee currently and/or next would be useful to expose via prometheus, so we can plan maintenance at the validator level (which is managing for us ~200-300 pubkeys) accordingly.

Describe the solution you'd like

Expose prometheus metric per pubkey in the validator metrics

Describe alternatives you've considered

I've looked at https://www.coincashew.com/coins/overview-eth/guide-or-how-to-setup-a-validator-on-eth2-mainnet/part-ii-maintenance/checking-my-eth-validators-sync-committee-duties already, but would like to have this via prometheus

Links:

• Prysmatic Labs code-review channel discord conversation with potuz and prestonvanloon