Add custom JSONDecoder property to HitsInteractor

[VladislavFitz]

Is your feature request related to a problem? Please describe 🙏

Described here. Client wants the Codable model variable names to be in camel case. HitsInteractor supports only the snake case since it uses the default JSONDecoder constructor, so the client might add CodingKeys per model.

Describe the solution you'd like 🤔 Add possibility to set a custom JSONDecoder property to HitsInteractor responsible for search hits decoding.