FilterTree

The UI filter tree - the representation the filter dialog renders and the backend stores in
PeopleList.Filter. Mirrors FilterTree in the frontend's
libs/common/types/Shared/filter.ts.

Groups are OR-ed, the rules inside a group are AND-ed.

{
    "groups": [
        {
            "rules": [
                {
                    "column": "string",
                    "condition": "string",
                    "value": null
                }
            ]
        }
    ]
}