Define job polling interval in env

Currently, the application uses an env variable to define the solid
cable polling interval, in order to allow deploying instances to
tweak some platform behaviors without code changes.

This proposal is to adopt the same strategy for the job queue polling
interval. The default value (if no env variable is defined) is the
same as it is now - 0.1 seconds - but if a deploying instance needs
to run a little slower, this will enable that.

Author: matt-bernhardt

config/queue.yml

@@ -7,7 +7,7 @@ default: &default
     - queues: "*"
       threads: 3
       processes: <%= ENV.fetch("JOB_CONCURRENCY", 1) %>
-      polling_interval: 0.1
+      polling_interval: <%= ENV.fetch("JOB_POLLING_INTERVAL", 0.1) %>
 
 development:
   <<: *default