Return trials to frontend only when they are used

In the backend, an Experiment is stored together with its generated trials in memory, after an Experiment was created in the frontend.

For the Experiments list view we don't need the trials but they are still returned.

For many Experiments with large number of trials this leads to unnecessary transfer of information, slowing down the application, especially when the instance has limited resources.

We should only return (and even generate) the trials if a user opens the Experiment detail view.

frontendの一覧ビュー向けにExperimentsがどのように保存され、返されるかを追跡し、そのフローをExperimentの詳細ビューと比較します。trialsがどこで生成され、転送されるかを確認します。一覧レスポンスでは未使用のtrialsを避けつつ、Experimentを開いた場合は引き続きtrialsが生成され、返されれば完了です。