As a user, I want to see Knappegruppe with the other buttons

[Ildest]

In the component panel, Knappegruppe is placed under Avansert. There is noe apparent advantage for the user in this placement, so @Annikenkbrathen and I suggest that we move Knappegruppe up with the other buttons, and create an Accordion called Knapper, where all button components reside.

Related issue #13305 and https://github.com/Altinn/altinn-studio/issues/13358#:~:text=own%20accordion%20tab%3F-,%2313358,-Open

### Tasks
- [ ] Create a nested accordion called Knapper where most buttons are placed today, and move all buttons into this accodion.
- [ ] Move the component Knappegruppe from Avansert to reside with the other buttons in the new accordion