[Feature Request]: Allow projects to be grouped

### What would you like to happen?

Migration: https://issues.apache.org/jira/browse/HOP-2970

I get longer lists of projects.  It would be cool if we could group them together in topics.
Perhaps we can simply add a "group topic" field in the project metadata.

It would allow the list of projects to be reduced dramatically by grouping them.

The current combo drop-down list would need to be replaced by a menu or even an action dialog.

### Issue Priority

Priority: 3

### Issue Component

Component: Hop Gui

Start in the Hop Gui project-selection flow and inspect how project metadata is represented and how the current combo drop-down is populated. Use the linked HOP-2970 migration for context; done means projects can be assigned to topics and selected through a grouped replacement for the current list.

Written by the indexing model from the issue text.