fix: improve liqoctl uninstall error message

this patch improves the liqoctl uninstall error message when the
pre-uninstall checks fail, by suggesting the user which command has to
be used to unpeer a cluster.

pkg/liqoctl/uninstall/handler.go

@@ -66,7 +66,10 @@ func (o *Options) Run(ctx context.Context) error {
 
 	s := o.Printer.StartSpinner("Running pre-uninstall checks")
 	if err := utils.PreUninstall(ctx, o.CRClient); err != nil {
-		s.Fail("Pre-uninstall checks failed: ", output.PrettyErr(err))
+		errMsg := fmt.Sprintf("Pre-uninstall checks failed: %s\n"+
+			"You can disable the active peerings with other clusters with the 'liqoctl unpeer' command.\n"+
+			"Check 'liqoctl unpeer --help' for further information.", output.PrettyErr(err))
+		s.Fail(errMsg)
 		return err
 	}
 	s.Success("Pre-uninstall checks passed")