Expand string type to have contentSchema, contentMediaType + contentEncoding

[ghandic]

Allow auto data generation to produce data from fake files with certain encoding

https://json-schema.org/understanding-json-schema/reference/non_json_data.html#id2

[ghandic]

Content Encoding - #55

For contentMediaType, since it isn't an explicit set of values it can take, we will need to think about making it extensible and/or heavy documentation of what is supported for the generation

[ghandic]

Closed as of #58

contentSchema is not currently planned to be supported.