Add updateMyDataset helper to useDatasetManager

Context

Epic: #391

Feature branch: feature/epic-refacter-use-dataset-manager-hook

Currently, we store and update the user-saved My Dataset using the context state myDataset and its setter setMyDataset.

This setter is used in the useDatasetManager hook and called from hook's methods (e.g., getDataset) on API requests.

In this issue, we want to create a wrapper helper method responsible for setting myDataset and to be called from the hook methods instead of directly invoking the context state setter.

Problem or idea

We should replace all setMyDataset calls within the hook with the new wrapper method described above.

Solution or next step

1. Add a new method updateMyDataset that accepts the dataset fetched from the API
2. Replace the setMyDataset calls with this newly added wrapper method