Feature Request Overview (mandatory - Complete while in New status){_}
{}What user goal or problem do you need to solve?{_} 
In RHOSP17.1, puppet-horizon provides an interface to customize WSGIDaemonProcess.
The default, `WSGIDaemonProcess apache display-name=horizon group=apache processes=4 threads=1 user=apache`, is really small for production.
For example, if the horizon uses legacy upload mode for glance, horizon call glanceclient to upload the image to glance. It is likely to consume all 4 processes when simultaneous image uploads happens. Then, liveness probe will kill the pods then then image upload will fail.

To prevent the such situation, a user needs to tune the number of process and number of pods.

In RHOSO18, the modification flexibility is reduced and to overcome the real production issue, we should implement this feature to tune the configuration.

Business justification (mandatory - Complete while in New status)
How would this feature benefit the customer?
By this feature, our customers can get the flexibility to tune Horizon pod and prevent the unexpected kill of horizon pod.

Functional requirements (mandatory - Complete while in New status){_}
{}What do you want the result of this feature to be? Add as many requirements as needed.{_}

•  Add an interface to tune items in WSGIDaemonProcess
•  Modify template to accept the tuned values.

Describe the customer impact
Without this RFE, horizon pods is easily to be killed by livevness probe when simultaneous large image upload happens.

(Optional) Point of contact

• Provide any additional points of contact for this feature request, such as an account executive, SA, or TAM: 
•  TAM

(Optional) Additional links
Original discussion was done at https://issues.redhat.com/browse/OSPRH-18633