test(e2e): add TLS listener rejectUnknownSNI test suite

Covers rejectUnknownSNI with and without a serverNames allow list,
verifying allowed/unknown/empty SNI handshakes via openssl s_client.

tests/e2e/testdata/tls/reject_sni.yaml

@@ -0,0 +1,11 @@
+services:
+- name: tls-reject
+  addr: :8443
+  handler:
+    type: http
+  listener:
+    type: tls
+    tls:
+      rejectUnknownSNI: true
+      serverNames:
+      - example.com