return error for non-existing resources

[Rdataflow]

Is your enhancement related to a problem? Please describe. opening a non existing cube IRI returns HTTP status 200 (success) whereas status 40x (error: not found) would be more appropriate.

Describe the solution you'd like opening a non existing cube returns status 40x (error: not found), so machines are informed of non-existing resources and can rely on this i.e. to enable basic link checkers work correctly

Describe alternatives you've considered do manual link checking :/

Usecases and impact automated link checking i.e. on opendata.swiss linked resources like https://opendata.swiss/de/dataset/lfi-themen-nach-eigentum-offentlich-privat featuring a link link e.g. https://visualize.admin.ch/en/browse?previous=%7B%22includeDrafts%22%3Afalse%7D&dataset=htps%3A%2F%2Fenvironment.ld.admin.ch%2Ffoen%2Fnfi%2Fnfi_C-94%2Fcube%2F2023.1&dataSource=Prod