feat: add a feature to flush SSH known hosts for VM

[flexiondotorg]

Quickemu exposes localhost:<port> (where is 22220 and upwards) for connecting to guest VMs over SSH. It is likely guest VMs will be deleted, and new guests will reuse ports previously assigned to past VMs.

This can result in Quickgui not being able to establish a SSH connection to a guest VM because the knownhost keys no longer match.

Therefore Quickgui should add a mechanism to remove knownhost keys for guest VMs using something like ssh-keygen -R [localhost]:22220. Better yet, a means to detect SSH connection are failing due to invalid knownhost keys and prompting to flush them.