fix metrics key
remove 'Created' from subscriber names
move tests to appropriate folder
fix constraint names
add IsLatest to HubType and Subscriber
add SubscriberRegistration and first test infrastructure
add HubSnaptshot Table.InsertRange
RegisterSubscribers_should_update_subscribers_table

opted for one test to update empty and then populated table because the setup for the latter was identical to the test for the former
use SubscriberRegistration to register subscribers
add PartitionSnapshot
fix Subscriber.Latest to work in partition dbs too
add Exists table ext that checks for count > 0
finish SubscriberRegistration.UpdatePartitions and extract interface
remove using
finish tests and full snapshot
let HubRegistration update partitions
rename QueueThreadMetricsLogger -> IntervalMetricsLogger
extract SystemMetricsLogger from IntervalMetricsLogger
remove unused field
finish SystemMetricsLogger

- remaining work is to add thresholds and potentially lock partitions to avoid duplicate collection of stats
- SystemMetricsLogger can be injected now and populated from settings
- QueuePrep now only enqueues and finishes