Provide an api to provision circuit-breaker instances dynamically

[reisenberger]

Possible enhancement: add an API for provisioning new circuit-breaker entities dynamically (as opposed to having breakers pre-defined in config).

Decision what to do then with the current initialize-breakers-from-configuration approach. Either:

• move it to StartUp, reading and provisioning pre-configured circuit-breakers from appsettings as a one-off startup operation; or
• remove the existing initialize-breakers-from-configuration approach. Probably retain the somewhat technical configuration parameters ConsistencyPriorityCheckCircuitTimeout, ConsistencyPriorityCheckCircuitRetryInterval and PerformancePriorityCheckCircuitInterval in appsettings, and just move the MaxConsecutiveFailures and BreakDuration parameters to a circuit-breaker provisioning API.