Add impersonationProxyServerPort to the Concierge's static ConfigMap

- Used to determine on which port the impersonation proxy will bind
- Defaults to 8444, which is the old hard-coded port value
- Allow the port number to be configured to any value within the
  range 1024 to 65535
- This commit does not include adding new config knobs to the ytt
  values file, so while it is possible to change this port without
  needing to recompile, it is not convenient

deploy/concierge/deployment.yaml

@@ -59,6 +59,7 @@ data:
         renewBeforeSeconds: (@= str(data.values.api_serving_certificate_renew_before_seconds) @)
     apiGroupSuffix: (@= data.values.api_group_suffix @)
     # aggregatedAPIServerPort may be set here, although other YAML references to the default port (10250) may also need to be updated
+    # impersonationProxyServerPort may be set here, although other YAML references to the default port (8444) may also need to be updated
     names:
       servingCertificateSecret: (@= defaultResourceNameWithSuffix("api-tls-serving-certificate") @)
       credentialIssuer: (@= defaultResourceNameWithSuffix("config") @)