Caching ciPipelineCreationInputs

Summary

When we implemented the prefill variables, we realized that the prefill variables calculation is slow due to external file fetching; local, project, remote, etc. Then, we implemented the ReactiveCaching. You can see the details in the app/services/ci/list_config_variables_service.rb file.

When we introduced pipeline inputs, we did not need it because it was a straightforward fetch-and-render mechanism. Now, we introduced external files for pipeline inputs. This will make the ciPipelineCreationInputs GraphQL query slower. We need to implement caching.