The table-based audit backend needs Raft to create its keyspace,
but the audit service must exist earlier so that CQL paths don't
silently skip auditing.
Split startup into two phases: construction and storage
initialization. Queries arriving between the two phases are
logged as errors.
This is a refactoring commit and the split sections will be
moved later in this patch series.
Refs SCYLLADB-1615
bc67dd0b82