Repeating groups - Help text for table headers.

### Description

When you have repeating groups, I want to be able to add help texts for table headers.
This is really helpful when you have the setting `editInTable ` set to `true`.
As shown in the example below.

### Additional Information

_No response_

Start by tracing the repeating-group table rendering and the editInTable setting in the frontend. Determine how table headers are configured and how help text is represented elsewhere; the work is done when repeating-group headers can display help text while editInTable is true, with coverage for the resulting behavior.

Written by the indexing model from the issue text.