Add build() overload that doesn't use Environment

Sometimes, you will want to configure and build a `Cluster` instance using `CassandraFactory`, but you won't have an `Environment` available.

The common-case here is when writing a `ConfiguredCommand` that uses Cassandra (e.g. for a utility to execute your applications' DDL statements).

While we have no `Environment`, we can still register health-checks and metrics, but we cannot manage the Cluster lifecycle, as there's no Environment to tie its lifecycle to.

This is broadly following the idiom used by the Liquibase Commands in `dropwizard-migrations` and the `DataSourceFactory` it uses to configure connections.