feat: add --hostname flag to customize the vm hostname

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

convert_options.go

@@ -34,6 +34,8 @@ type convertOptions struct {
 	keepCache bool
 	platform  string
 	pull      bool
+
+	hostname string
 }
 
 func (o *convertOptions) hasGrubBIOS() bool {
@@ -127,3 +129,9 @@ func WithPull(b bool) ConvertOption {
 		o.pull = b
 	}
 }
+
+func WithHostname(hostname string) ConvertOption {
+	return func(o *convertOptions) {
+		o.hostname = hostname
+	}
+}