Implement WorkerActivitiesPerSecond

[sokada1221]

Implements WorkerActivitiesPerSecond as per documentation.
closes #553

Key points:

• Implements WorkerActivitiesPerSecond with Throttler at PollTaskExecutor
• Throttler evaluation interval defaults to 1s when interval per message is less than 1ms (i.e. will implicitly allow more bursts)

Test results:

• Unit tests
• Local integration tests with workerActivitiesPerSecond set to 0.00001, 0.3, 0.5, 1, 2, 1000, 2000
• Local integration tests without taskListActivitiesPerSecond set