fix #4778: fix boolean type check for json parameters over the api

fix #4778: fix boolean type check for json parameters over the api

if a real json boolean is sent via the api, $value is a
JSON::PP::Boolean here instead of a string/scalar

so we should validate that too

the $value itself can be used normally in conditions like
----
if ($value) {
----

if the value is stringified, the result is either '1' or '0' so even if
we have some explicit checks like that it should not make a problem

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>