test(e2e): regression for Gost-Target destination-policy bypass

Adds TestGostTargetPolicyBypass: a service-level bypass blacklists the
echo server; verifies the control request is 403, a checksum-valid
Gost-Target header naming an allowed authority cannot reach the blocked
backend, and a malformed header is fail-closed. Verified to catch the bug
by reverting the fix (exploit returned the backend response).

tests/e2e/testdata/http/server_policy_bypass.yaml

@@ -0,0 +1,18 @@
+# Service-level destination bypass (blacklist) on an HTTP forward proxy.
+# Blocks the echo server's address ({{.ServerAddr}}). Used by
+# TestHTTPProxyGostTargetPolicyBypass to verify that a Gost-Target header
+# cannot separate the authority evaluated by the policy from the authority the
+# transport dials.
+bypasses:
+  - name: bypass-0
+    matchers:
+      - "{{.ServerAddr}}"
+
+services:
+  - name: http-policy
+    addr: ":8080"
+    handler:
+      type: http
+    listener:
+      type: tcp
+    bypass: bypass-0