💡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.

Inspect cmd/cloudflared/linux_service.go around line 64, the entry point linked in the issue, and review how the systemd service is generated. Use the Environment= directive so the tunnel token is not exposed in the process arguments, then verify the resulting service behavior and that the token no longer appears in ps output.

Written by the indexing model from the issue text.