feat: App card's style enhancement

[LinaYahya]

• style enhancement includes:
  • extend card content height
  • remove shifting down when selecting an app card
• toggle selection on card itself
• add back button from custom app selection

closes #811

[spaenleh]

@LinaYahya
I took the liberty to propose some changes:

• use outline instead of border to create the selection border
  • this allows to avoid layout shifts and does not affect the box model see below the white outline when there is no border (transparent)

With border:

With outline

• use Graasp button without re-styling for the "Back to app list"
• use a stack to create spacing between the form fields
• remove <br />
• fuse conditional elements controlled by isCustomApp
• use Grid2 for grid layout and make number of items responsive (1 when small, 2 when medium, 3 when large)
• add a description for the custom app card
• improve AppCard prop to make it more generic and type the function appropriately
• added some flexbox magic to ensure the app names are at the same height (height: "100%" was not centering the card content)