Migrate completely from go-boost-util types to Attestant types

[avalonche]

Post capella, we can clean up by removing all Bellatrix code paths in the relay especially in the wrapper types.

This makes it easier to migrate completely from go-boost-utils and to attestant types. Right now there is still mixed bellatrix types that can be removed from the relay.

[avalonche]

done and rest of the clean up covered by #489