* Replaced ClusterMetricSink's cluster name with an atomic.Value.
This should permit go-race tests to pass which seal and unseal
the core.
* Replace metric sink before unseal to avoid data races.
* Add new Telemetry config options
Add cluster_name, maximum_gauge_cardinality, and usage_gauge_period
configuration options to the config stanza.
Update unit tests.
Document.
Co-authored-by: Mark Gritter <mgritter@hashicorp.com>
