Create a table where the users can select previously created groups

## Description
App developer would like to produce a table that lists groups created by the users earlier in the form process. The users should be able to select each row in the table in relation to a new question.

Could be solved with a checkboxlist.
* Needs a way for the user to add new elements to the list

## Screenshots

## Considerations
* Should the user be able to create new groups when in this state?

## Acceptance criteria
> Describe criteria here (i.e. What is allowed/not allowed (negative tesing), validations, error messages and warnings etc.)

## Specification tasks

- [ ] Development tasks are defined
- [ ] Test design / decide test need

## Development tasks
> Add tasks here

## Definition of done
Verify that this issue meets [DoD](https://confluence.brreg.no/display/T3KP/Definition+of+Done#DefinitionofDone-DoD%E2%80%93utvikling) (Only for project members) before closing.

- [ ] Documentation is updated (if relevant)
- [ ] Technical documentation (docs.altinn.studio)
- [ ] User documentation (altinn.github.io/docs)
- [ ] QA
- [ ] Manual test is complete (if relevant)
- [ ] Automated test is implemented (if relevant)
- [ ] All tasks in this userstory are closed (i.e. remaining tasks are moved to other user stories or marked obsolete)

Start by reviewing the existing group-creation flow and the proposed checkboxlist/table behavior described in the issue. Clarify whether users may create groups while selecting, then define acceptance criteria, development tasks, and test needs; done should include selecting previously created groups and adding new list elements.

Written by the indexing model from the issue text.