Add "on" and "off" in boolean validation.

[dalsochio]

validation/src/Rules/Boolean.php

Line 21 in ff003a3

return \in_array($value, [\true, \false, "true", "false", 1, 0, "0", "1", "y", "n"], \true);

Some HTML inputs return "on" and "off" for true or false.

Would it be possible to add these two to the boolean types?