Change hint for multiple datasets to be clear that single input is allowed

Summary of Changes

Changes the hint for a Multiple Dataset input from "Multiple Datasets" to "Dataset(s)" to be clearer that a single dataset is allowed as an input along with multiple datasets.

Checklist

• The MR has a clear and concise title
• Code is self-documented and follows style guidelines.
• Automated tests are written and pass successfully.
• Regression tests (e.g. manually triggered system tests, manual GUI/tool tests, ...) are performed to make sure the MR does not break anything (when applicable)
• Readme file is present and up-to-date.

Documentation Updates

Additional Notes

Closes #123 (closed)