gatus: serve s2.rubenhensen.nl through the Gateway as well

First app on the Gateway API: an HTTPS listener for s2.rubenhensen.nl using the existing certificate in the gatus namespace, an HTTPRoute, and a ReferenceGrant for the certificate. Plain HTTP on the Gateway now redirects to HTTPS. The Ingress stays until the switch-over.

gateway/https-redirect.yaml

@@ -0,0 +1,17 @@
+# Plain HTTP only redirects to HTTPS. cert-manager's HTTP-01 challenge
+# routes name an exact hostname, so they win over this catch-all.
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: https-redirect
+  namespace: envoy-gateway-system
+spec:
+  parentRefs:
+  - name: homelab
+    sectionName: http
+  rules:
+  - filters:
+    - type: RequestRedirect
+      requestRedirect:
+        scheme: https
+        statusCode: 301