feat: add comprehensive HTTP e2e tests covering connector, TLS, probeResist, idleTimeout, and UDP relay

Adds 12 new HTTP handler test scenarios: HTTP connector (no-auth, auth, TLS
upstream), CONNECT tunnel (no-sniffing, bypass-403), probeResist (host, web,
file, knock), idleTimeout, and UDP relay over HTTP. Introduces
RunGostContainerWithFiles helper for mounting extra files into test containers.

tests/e2e/testdata/http/client_connector_auth.yaml

@@ -0,0 +1,23 @@
+services:
+- name: http-proxy
+  addr: :8080
+  handler:
+    type: http
+    chain: http-chain
+  listener:
+    type: tcp
+
+chains:
+- name: http-chain
+  hops:
+  - name: hop-0
+    nodes:
+    - name: node-0
+      addr: {{.ServerAddr}}
+      connector:
+        type: http
+        auth:
+          username: user
+          password: pass
+      dialer:
+        type: tcp