Before this change when running cloudflare tunnel command without any
subcommand and without any additional flag, we would spin up a
QuickTunnel.
This is really a strange behaviour because we can easily create unwanted
tunnels and results in bad user experience.
This also has the side effect on putting more burden in our services
that are probably just mistakes.
This commit fixes that by requiring user to specify the url command
flag.
Running cloudflared tunnel alone will result in an error message
instead.