Add support for features to contain a customization schema

[lonhutt]

We have a need to programmatically validate/constrain the set of customizations available for a given feature. Even if it's as simple as making sure that an optional schema.json (json schema) file exists within the packaged feature would be helpful here.

[Ali3219]

0x08Dc6385204D434f0A407902eF6A271de0366912