Specification imports for phase0 were aliased as 'spec'. Due to the
mechanism decided upon to manage structs that vary beteween hard forks
this is no longer useful, so this removes the alias in preparation for
the Altair hard fork.
This reintroduces prometheus metrics for the account manager module.
The metrics track the validating state of each account, and are found
under the `vouch_accountmanager_accounts_total` metric. The metrics are
differentiated using the `state` label.