Manual CSV import

Description - During a CSV import, there should be an option to either append the data to the existing dataset or overwrite it.

Why is this feature important to you - This option is important because it prevents data loss and ensures proper data management. Without a clear choice between appending and overwriting, users might accidentally overwrite valuable existing data or create duplicate entries.

How would you like the feature to work - When manually uploading a file with data for an audience, one of the steps should include an option to choose whether to append or overwrite the data.

Current Behaviour - Currently, when manually uploading data, it's unclear whether the data is being appended or overwritten.