post https://{server_url}/{api_key}/eth/v1/validator/sync_committee_subscriptions
Subscribe to a number of sync committee subnets
Sync committees are not present in phase0, but are required for Altair networks.
Subscribing to sync committee subnets is an action performed by VC to enable network participation in Altair networks, and only required if the VC has an active validator in an active sync committee.