[Feature Request]: Create GUI method to have widgets end up in a group

### What would you like to happen?

Import: https://issues.apache.org/jira/browse/HOP-4562

On occasion we want a Hop GUI widget to end up in a group.

When we automatically generate user interfaces we want to do the same and as such it would be useful to have the `@GuiWidgetElement` annotation support this.

### Issue Priority

Priority: 3

### Issue Component

Component: Hop Gui

Start by locating the @GuiWidgetElement annotation and the Hop GUI code that processes it. Determine how generated widgets are assigned to groups and define completion as annotation-driven grouping working for automatically generated user interfaces, with suitable tests added for the behavior.

Written by the indexing model from the issue text.