Groupable navigation

[IamSAB]

If i got a lot of lists, the main navigation gets quite confusing. I would like to be able to group lists similar to how fields are grouped. I thought, you could add that directly to the lists keystone config like:

// keystone.ts
export default config({
  db: {},
  lists: {
     list(),
     ...group({
        label: 'Group 1',
        icon: 'group',
        description: 'First Group',
        collapsed: true,
        lists: [ list(), list()]
     }),
  },
}

A further improvement would be able to add an icon to the group and choose wheter it is collapsed by default.

This would not even be a breaking changes because when reading the list, we only have to check wheter its a list or group and unpack if a group.

As a step further, you could also implement nested groups,