Hierarchical dimensions: Group together related values of a dimension

[japsu]

Consider, for example, dimension room in event ropecon2024, that has values like

              {
                "slug": "halli-3-perhealue",
                "title": "Halli 3 Perhealue"
              },
              {
                "slug": "halli-3-tanssiharjoitussali",
                "title": "Halli 3 Tanssiharjoitussali"
              },
              {
                "slug": "halli-3-turnaussali",
                "title": "Halli 3 Turnaussali"
              },
              {
                "slug": "halli-3-vapaa-pelialue",
                "title": "Halli 3 Vapaa pelialue"
              },

There's a lot of values in the dimension, and some of them have a hierarchy.

We would like to group together related values of the dimension, so that for example sub-areas of Hall 3 would be somehow visually together. Perhaps also hide sub-areas until their parent is selected?

In the GraphQL API this could be done eg.

              {
                "slug": "halli-3",
                "title": "Halli 3"
                "children": [
                  {
                    "slug": "halli-3.tanssiharjoitussali",
                    "title": "Halli 3 Tanssiharjoitussali"
                  },
                  {
                    "slug": "halli-3.turnaussali",
                    "title": "Halli 3 Turnaussali"
                  },
                  {
                    "slug": "halli-3.vapaa-pelialue",
                    "title": "Halli 3 Vapaa pelialue"
                  },
                ]
              },

and the hierarchy also shown in the slug using a dotted path.