add validators

add main validator to hold the shared function between all validators,
and add a CdnFacadeValidator to hold the validation of the CdnFacade
class.
add validation

validate the asset() function doesn't have an empty $path
rename configuration cass (validator) to ProviderValidator

and make it extends validator
update usage of Vinelab\Cdn\Validators\Contracts\Configurations
to become Vinelab\Cdn\Validators\Contracts\ProviderValidator

after renaming the validator class
add exception class to be trow when a function input is missed

class name is EmptyInputException
add missed public functions to validator interfaces
update the FacadeTest after injecting new dependency to the CdnFacade
class.

The new dependency is the validator class
add if condition to check if $path exist in the asset() function
add testing for null asset parameter
rename the exception EmptyInputException to EmptyPathException
remove checkIfEmpty from the Validator class