* initial validator attesthead rewrite based on proposer rewrite
* proceed with fetching committees and tree hashing the canonical head at assigned attester slot
* complete filling the properties of attestation data and all associated root hashes
* add when to attest todo
* finish entire attester client logic
* tests with mocks checked in
* tests passing in client
* stubbed out server implementation
* fixed build due to old property
* regen mocks with new mockgen version
* fixed broken tests
* complete bazel build fix
* address some review comments
* deep proto test
* tests passing after checking for empty committee and crosslink root
* address nishant comments
