Add how-to for configuring XFF handling

[HappyTetrahedron]

No description provided.

[simu]

This page should be part of https://github.com/appuio/managed-openshift-docs (the end-user docs for APPUiO Managed OCP4, available at https://docs.appuio.ch/managed-openshift/) and not kb.vshn.ch/oc4.

[simu]

Probably makes sense to note that the annotations can also be set on Ingress objects which are managed by the ingresstoroute controller

[simu]

Suggested change

	This how-to explains how to configure the ingress' handling of the forwarded headers (`Forwarded` and `X-Forwarded-For`) on a per-route basis.
	This how-to explains how to customize how the forwarding headers (`Forwarded` and `X-Forwarded-For`) are handled by the OpenShift ingress router on a per-route basis.

[simu]

Suggested change

	* *`append`*: By default, the ingress is configured to append the headers to any existing headers. If `Forwarded` and `X-Forwarded-For` headers are already present when the ingress receives a request, the existing values are preserved, and new values are appended by the ingress.
	* *`append`*: By default, the OpenShift router is configured to append the headers to any existing headers.
	If `Forwarded` and `X-Forwarded-For` headers are already present when the OpenShift router receives a request, the existing values are preserved, and new values are appended by the router.

[simu]

Suggested change

	* *`replace`*: If forwarded header handling is set to `replace`, any existing forwarded headers are discarded. Only the headers set by the ingress will be available.
	* *`replace`*: If forwarded header handling is set to `replace`, any existing forwarded headers are discarded.
	Only the headers set by the OpenShift router will be available.

[simu]

Consider using the following formatting:

Suggested change

	* *`append`*: By default, the ingress is configured to append the headers to any existing headers. If `Forwarded` and `X-Forwarded-For` headers are already present when the ingress receives a request, the existing values are preserved, and new values are appended by the ingress.
	`append`:: By default, the ingress is configured to append the headers to any existing headers. If `Forwarded` and `X-Forwarded-For` headers are already present when the ingress receives a request, the existing values are preserved, and new values are appended by the ingress.

[simu]

Suggested change

	* *`never`*: If forwarded header handling is set to `never`, the ingress will never set these headers, and leave any existing headers untouched.
	* *`never`*: If forwarded header handling is set to `never`, the OpenShift router will never set these headers, and leave any existing headers untouched.

[simu]

Suggested change

	* *`if-none`*: If forwarded header handling is set to `if-none`, the ingress will only set the headers if they're not already present. If any headers are present, they're left unchanged.
	* *`if-none`*: If forwarded header handling is set to `if-none`, the OpenShift router will only set the headers if they're not already present.
	If any headers are present, they're left unchanged.

[HappyTetrahedron]

Closed in favor of appuio/managed-openshift-docs#7