Use error code instead of error message

[eskombro]

As referenced here meilisearch/meilisearch#683 MeiliSearch will rely now on error codes instead of error messages. This makes it possible to modify error messages without having an impact in the SDK behavior. Python SDK relayed in error messages, specially when trying to create an index that exists already in the MeiliSearch instance.

The MeiliSearchApiError should now find the error code, error message and error link pointing to the documentation.