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/server_headers.yaml

@@ -0,0 +1,25 @@
+bypasses:
+- name: bypass-0
+  matchers:
+  - 0.0.0.0/0
+
+services:
+- name: http-headers
+  addr: :8080
+  handler:
+    type: http
+    auther: auther-0
+    metadata:
+      header:
+        X-Proxy-Info: gost-e2e
+        X-Custom: test-value
+      proxyAgent: gost-e2e/1.0
+  listener:
+    type: tcp
+  bypass: bypass-0
+
+authers:
+- name: auther-0
+  auths:
+  - username: user
+    password: pass