deploy-tiproxy: Fix config section for session tokens (#2947) (#2952)

Author: ti-chi-bot

en/deploy-tiproxy.md

@@ -71,6 +71,7 @@ If you need to deploy TiProxy for an existing TiDB cluster, follow these steps:
               - name: sessioncert
                 mountPath: /var/session
             config: |
+              [security]
               session-token-signing-cert = "/var/session/tls.crt"
               session-token-signing-key = "/var/session/tls.key"
         ```

zh/deploy-tiproxy.md

@@ -71,6 +71,7 @@ summary: 了解如何在 Kubernetes 上为已有 TiDB 集群部署负载均衡 T
               - name: sessioncert
                 mountPath: /var/session
             config: |
+              [security]
               session-token-signing-cert = "/var/session/tls.crt"
               session-token-signing-key = "/var/session/tls.key"
         ```