Better management for the PhpKafkaConsumerCommand options

[joesantos418]

As pointed out by @DelBianco in the review for #9, we need to handle the options for the PhpKafkaConsumerCommand better. Currently the option "topic" requires an array while giving the impression it requires a string and returning no specific error feedback (there is a generic error, though). We should figure out a better way to handle it.