The plugin does not respect the job quiet period

We have 2 jobs triggering from a single pull request (`A` and `B`).
Job `B` depends on job `A`, meaning job `A` has to finish before job `B` starts.
We have configured a blocking job for `B` to be `A`, but it can only block if job `A` is in the queue.

Some of the times job `B` is added to the queue faster than job `A` and because job `A` is not in the queue, job `B` starts (and fails).

We wanted to use a quiet period for job `B` to make sure job `A` is put to the queue before job `B` is considered for starting.
There are 2 places to set the job quiet time, on a global Jenkins configuration and on the Job itself.

The plugin respects the global configuration but doesn't respect the job quiet period configuration as can be seen from this line:
https://github.com/jenkinsci/ghprb-plugin/blob/4e86ed47a96a01eeaa51a479ff604252109635f6/src/main/java/org/jenkinsci/plugins/ghprb/GhprbTrigger.java#L458

The `job` object also has a `getQuietPeriod()` function which can be used in combination with the global settings. (if the job quiet period is not set, use the global, otherwise use the job setting)

Start in src/main/java/org/jenkinsci/plugins/ghprb/GhprbTrigger.java at line 458, where the quiet period is selected. Check how the global setting is used and how the job's getQuietPeriod() can provide an override. Done means a configured job quiet period is respected, with the global setting used when no job-specific value is set.

Written by the indexing model from the issue text.