Implement PeerDAS subnet decoupling (aka custody groups)

[jimmygchen]

Issue Addressed

#6709

Spec: ethereum/consensus-specs#3832

Proposed Changes:

On startup, we construct NetworkGlobals and compute sampling subnets and sampling columns from NodeId - this remains the same but the computation logic has been updated to compute these from custody groups. (node_id => custody_groups => subnets and columns)

• Introduce "custody groups" and compute custody subnets and columns with custody group.
• Change custody_subnet_count (csc) to custody_group_count (cgc) in MetaData and ENR. (spec)
• Add a custody group to subnet mapping in PeerManager to avoid re-computing it when setting peer subnets based on their custody groups.
• The sampling_size computation logic is has been updated to be base on custody groups instead of custody subnets. code (spec update)
• Refactored sampling_size and custody_group_count logic into ChainSpec to keep them in one place.