Reorganize contract test again to better accommodate existence of GraphQL queries.

With the introduction of GraphQL queries, the need to organize and distinguish between GraphQL and REST tests has come up to keep the suite maintainable. This issue will be used to track the work to address this.

The following updates are needed:

• Updates consumer tests to use async calls and updating specs to use await for these async calls.
• Moves given/state attribute value to the fixtures for consistency between REST and GraphQL tests.
• Renames state files to use show_state, index_state, new_state, etc.
• Moves merge_request providers to be nested under show folder.
• Combines the 3 merge_request state files into one merge_request/show_state file.
• Updates rake task file path variables to reduce duplication.