Allow Set of NGINX Variables for RequestHeaderModifier

[mpstefan]

trafficstars

As a user of NGF I want to be able to use NGINX variables in to change the header of requests into NGF So that I can use the information contained with the request to set a header before forwarding the request to the upsteam.

Acceptance

• NGF allows the use of any NGINX variables contained within a list in the set value of a RequestHeaderModifier object.
• When an NGINX variable is used to define the value of a header within a RequestHeaderModifier, the header is set to the variable value at runtime.
• The only variable allowed is $request_time.