[Bug]: Enhanced JSON output - documentation improvement and/or missing functions

### Apache Hop version?

2.13

### Java version?

17.0.2

### Operating system

Linux

### What happened?

**Group key tab**
- better description: _This tab is used to define the key fields used for grouping the other fields in JSON fragments. Those fields will also be forwarded to the next transform, and the input stream must be sorted by those fields in order to make the groups correctly_
- there is currently no _Get Fields_ button on the tab. But it would be better to add this button, rather than strip it out from the documentation... (see also #5167)
- it seems that the _Element name_ colums is actually not used

**Fields tab**
- description for _Element name_: _the key name to use in JSON for this field (it can be different from the actual field name)_

### Issue Priority

Priority: 3

### Issue Component

Component: Hop Gui, Component: Transforms

Start by locating the Enhanced JSON transform implementation and its documentation, focusing on the Group key and Fields tabs. Verify whether Element name is used and whether a Get Fields button is missing; done means the tab descriptions and supported behavior are consistent with the resolved design.

Written by the indexing model from the issue text.