💡Use `TUNNEL_TOKEN` for systemd service so that TOKEN is not visible on `ps`

**Describe the feature you'd like**
Per title.

**Describe alternatives you've considered**
Are there any alternatives to solving this problem? If so, what was your experience with them?

**Additional context**
https://github.com/cloudflare/cloudflared/blob/f27418044ba359a17995166034d900c11aa50008/cmd/cloudflared/linux_service.go#L64

Can use `Environment=` directive.

检查 cmd/cloudflared/linux_service.go 第 64 行附近、issue 中链接的入口点，并审查 systemd 服务的生成方式。使用 Environment= 指令，使隧道令牌不会暴露在进程参数中，然后验证生成的服务行为，并确认令牌不再出现在 ps 输出中。

由索引模型根据 Issue 内容生成。