Revision 5e4811a0a3308befeca93953c283025cb3c8a3cb

Improved relation list field schema

Depending on the selectable content types & selection limit, the field yields a different type:
- one type, one item: one item of the constrained type ("File")
- one type, multiple items: a list of the constrained type ("[Files]")
- multiple types, single item: one DomainContent
- multiple types, multiple items: a list of DomainContent

```
{
test {
relationTest(id: 248) {
singleFileRelation {
name
file { uri }
}
multiFilesRelation {
name
file { uri }
}
multiTypesSingleItem {
... on SomeDomainType {}
... on SomeOtherDomainType {}
}
multiTypesMultiItems {
... on SomeDomainType {}
... on SomeOtherDomainType {}
}
}
}
}
```