20680: Rework worker settings for new controller behavior

20680: Rework worker settings for new controller behavior

We now have separate values for concurrent requests and queued
requests.  Ensure the arvados, passenger and nginx configurations align
with the correct values.

Renamed CONTROLLER_NGINX_WORKERS to CONTROLLER_MAX_WORKERS

Renamed CONTROLLER_MAX_CONCURRENT_REQUESTS to
CONTROLLER_MAX_QUEUED_REQUESTS

Adjusted config.yml defaults to reflect that MaxConcurrentRequests
means something different.

Arvados-DCO-1.1-Signed-off-by: Peter Amstutz <peter.amstutz@curii.com>