Add a --rm flag to "inletsctl create" for a temporary tunnel

We should add a --rm flag to "inletsctl create" for when users need a temporary tunnel.

The use-case would be that I want to share my blog i.e. 127.0.0.1:4000 with a friend or colleague, but I don't want to be billed for the DigitalOcean VM beyond my 1-2 hours of uptime.

I'd run a command similar to `docker run --rm` which removes the tunnel immediately after I hit control + c or exit.

We'd have something like this, but it'd need to work with inlets-pro too:

OSS:

```
inletsctl create --rm --upstream http://127.0.0.1:4000

Your IP is: X
Starting "inlets client" now, hit control+c to delete the tunnel.
```

Pro:

```
inletsctl create --rm --license $LICENSE --remote-tcp=http://127.0.0.1
Your IP is: X
Starting "inlets-pro client" now, hit control+c to delete the tunnel.
```