add mock response to test json rpc errors

[mdtanrikulu]

Motivation

The goal is to be able to test any json-rpc errors and consequences afterwards. I needed such modification while writing test cases for a middleware.

Solution

• Added new enum called MockResponse, instead of passing the Value, now we pass this enum as a response type.
• MockProvider now checks the response types with match and treats accordingly.
• new fn called push_response helps pushing the JsonRpcError as the next response.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[DaniPopes]

Thanks!