Url query params should be represented by a dedicated data type

[thkoch2001]

e.g. https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams

Currently they are represented by [(String, String)]

• which is a missing opportunity for type safety and a more informative type name
• and also does not allow to represent keys without values, e.g. ?something&with=value&more=stuff