Ability to Duplicate Rows in Repeating Groups

### Description

I ropose a usability enhancement for repeating groups (table-like components) that would streamline the data entry process for users.

**Current Behavior**
Users must manually fill out each row, even when multiple rows have identical or nearly identical content. This is time consuming and increases the likelihood of user errors.

**Proposed Change**
Add a “Duplicate Row” (or “Copy Row”) function that allows the user to quickly copy the contents of an existing row and create a new row with the same data.

The duplicated row should allow editing so users can adjust only the fields that differ.

**Benefits**
- Significantly reduces repetitive manual data entry.
- Improves efficiency and user satisfaction.
- Minimizes errors by reducing the number of times users must retype the same information.

### Additional Information

_No response_

No files, tests, or entry points are named in the issue. Start by locating the repeating-group implementation and its existing row-add behavior, then determine how row values are represented and copied. Done means users can duplicate an existing row, edit the copied values independently, and have coverage for the new interaction.

Written by the indexing model from the issue text.