Read connectionsPerEndpoint when connecting

[jking-stripe]

Context

Adjusts how and when the connectionsPerEndpoint property gets read. Rather than reading the property early, this change delays reading it until attempting to connect to previous stages. This will allow for configuration on a per-job basis.

This also includes some additional adjustments to remove minConnectionsToSubscribe as a parameter of the WorkerPublisherRemoteObservable constructors, neither of which use it. This allows for the removal of a numWorkersAtStage helper.

Checklist

• ./gradlew build compiles code correctly
• Added new tests where applicable
• ./gradlew test passes all tests
• Extended README or added javadocs where applicable

[kmg-stripe]

@Andyz26 - could you have a look when you get a chance? thanks!