add support for validating boolean values

[muneer-memon]

the transformValidationOption allows to convert string to type values using enableImplicitConversion option

const transformedValidatedValues = await transformAndValidate(
schema,
requestPayload,
{ transformer: { enableImplicitConversion } } // E.g. string numbers will be converted to type number
);
however there is one issue. if your schema specifies one boolean property and the request payload pass any string other than 'true' or 'false' the transformer converts it into true.