Add support for 'schema.registry.url' property in ConsumerConfig and ProducerConfig schemas

[msouce]

Thank you so much for creating and maintaining this library – it's really a pleasure to use.

This PR adds an optional consumer and producer config key, schema.registry.url, so Franzy's Schema validations can play nice with the Confluent Platform.

Per Confluent's documentation, the schema.registry.url property should be in the general Properties passed to the Kafka Consumer on instantiation.

Currently, things work out of the box. It'd just be nice to have Schema validations work, too, instead of throwing an error.

Would also love to hear thoughts on potentially more idiomatic ways to accomplish this.

[ymilky]

Thanks, I've been away for a few days on business and I'll have a look. The documentation for the configuration properties is often missing some of the keys, so usually it's best to check the official source directly. I'll verify.

Regarding schema, I'll have a look. You may be using an older version and I certainly need to push some new versions. In the latest build I believe I removed the required schema checks. There's been some debate whether there should be one related to config or not. My feeling is the schema types should be there but since schema allows you to to globally toggle checks, there's not necessarily a need to force it to be "on" via the API. Let me know if you have any thoughts.

[lbradstreet]

Another option if things aren't going to be kept up to date, is to allow {s/Keyword s/Any} as possible values, which will allow any unknown properties to be used and still schema check. This is not really ideal as typo'd properties will be missed, but at least it can be worked around until franzy is updated on each occasion.