gost: bump x to v0.13.9, relay to v0.6.2; add PHT e2e tests

- go.mod: x v0.13.8 → v0.13.9, relay v0.6.1 → v0.6.2
- tests/e2e/pht_test.go: 3 test cases (basic tunnel, PHTs, heartbeat)
- tests/e2e/testdata/pht/: client/server and client_phts/server_phts YAML configs

tests/e2e/testdata/pht/client_connector_phts.yaml

@@ -0,0 +1,20 @@
+services:
+- name: phts-proxy
+  addr: :8080
+  handler:
+    type: http
+    chain: phts-chain
+  listener:
+    type: tcp
+
+chains:
+- name: phts-chain
+  hops:
+  - name: phts-hop
+    nodes:
+    - name: phts-node
+      addr: {{.ServerAddr}}
+      connector:
+        type: http
+      dialer:
+        type: phts