PIP-2675: Disable Batching and Force Global configuration

[Baliedge]

https://mailgun.atlassian.net/browse/PIP-2675

• Batching functionality may be disabled by configuration Behaviors.DisableBatching = true.
  • Frees up some resources, goroutines.
  • Eliminates small delay in each request as batches are assembled and dispatched that may not be beneficial if batch size is typically small.
• Force global behavior on all rate checks by configuration Behaviors.ForceGlobal = true.
  • Global behavior is unaffected by DisableBatching setting.
• Change GlobalSyncWait default from 500µs to 500ms to reduce global sync traffic.
• Remove unnecessary buffer from WorkerPool command channels.
• Remove extraneous tracing detail.
• Metric updates
  • WorkerPool metrics:
    • Renamed gubnernator_pool_queue_length to gubernator_worker_queue_length.
    • Added gubernator_command_counter: Counter of commands executed in WorkerPool.
    • Removed gubernator_check_counter.
      • Redundant. Use gubernator_getratelimit_counter{calltype="local"}.
  • Global behavior metrics:
    • Added gubernator_global_queue_length: Size of global broadcast queue.
    • Renamed gubernator_broadcast_durations to gubernator_broadcast_duration.
    • Added gubernator_broadcast_counter: Rate of global broadcasts. Label condition may be timer|queue_full to indicate what triggered the broadcast.
    • Changed gubernator_concurrent_checks_counter from summary to gauge type.
  • Batch behavior metrics:
    • Renamed gubernator_async_durations to gubernator_async_duration.
    • Renamed gubernator_asyncrequest_retries to gubernator_batch_retries.
    • Renamed gubernator_queue_length to gubernator_batch_queue_length.
      • Changed from summary to gauge type.

[thrawn01]

A few nit picks, but looks good!