Move X-Forwarded-Port variable to the location context

Resolves issue #4038 where the X-Forwarded-Port header would be set to the value of the https listening port if all of the following settings were satisfied:
- The ingress controller was started with a non-default HTTPS port set with the `--https-port` argument
- An ingress is created having:
  - the `nginx.ingress.kubernetes.io/auth-url` annotation set
  - TLS enabled

This commit solves this issue by moving the setting of the `pass_server_port` variable from the server, one level down to the location context.

test/e2e-image/namespace-overlays/forwarded-port-headers/deployment-patch.yaml

@@ -0,0 +1,12 @@
+- op: replace
+  path: /spec/template/spec/containers/0/ports/0/containerPort
+  value: 1080
+- op: replace
+  path: /spec/template/spec/containers/0/ports/1/containerPort
+  value: 1443
+- op: add
+  path: /spec/template/spec/containers/0/args/-
+  value: --http-port=1080
+- op: add
+  path: /spec/template/spec/containers/0/args/-
+  value: --https-port=1443