Limit the number and size of entries

[guillaumerose]

One attacker could possibly call the admin-helper to add a large number of host files entries or very long DNS names.
We should do something for that.

original comment: crc-org/crc#1793 (comment)

Hmm, any process in the VM can fill the host root filesystem, and maybe slow down name resolution? (dunno if huge /etc/hosts has a noticeable impact on name resolution). I did not check the admin-helper code, but we can limit the number of aliases we add to a few hundreds, and also limit their individual size (which is done already I think), which would address this concern.