limactl start with VM name type creates new default VM

Both the `limactl start` and `limactl create` commands will create a VM. If a user has an existing VM and attempts to use the `limactl start` command and spells the VM name incorrectly, it will create a new default VM with 100GiB disk. This could be a potentially bad situation where a user/system is creating multiple VMs declaratively and without hundreds of GiB of free disk space. I would reconsider this behavior and not create a new VM using the `start` command without at least a warning or prompt to continue. Preferred behavior would be to encourage users to use the `create` command to create VMs and the `start` command to start them.