1. Proposed title of this feature request
Allow custom modification of HAproxy router templates in openshift-ingress
2. What is the nature and description of the request?
Right now the HAproxy config inside openshift-ingress pods is completely managed and it's not possible to make changes or add custom plugins as it was possible in 3.11. A way of allowing injection of custom configuration is requested
3. Why does the customer need this? (List the business requirements here)
In an Openshift 3.11 cluster the router template has been customized in order to build route specific user lists through "userlist" HAProxy directive driven by a custom route annotation, then different types of routes backend have been modified in order to add, if the custom annotation is present for the route, an "acl" [2] check using the the http_auth [3] expression against the route's userlist and then validating it with http-request auth unless <acl>" [4] directive.  This is not possible to modify right now in an Openshift 4.x cluster.

[1] userlist - https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#3.4-userlist
[2] acl - https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#7.1
[3] http_auth - https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#7.3.6-http_auth
[4] http-request - https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#4.2-http-request

4. List any affected packages or components.
N/A