Fix required fields in swagger

[JonasKellerer]

Some fields are marked with an asterisk and are therefore required in the Swagger-UI. However, not all required fields are marked. This should be changed. For example, for a nucleotideMutation Request, 'mutation', 'proportion' and 'count' should be required.

This was found in https://github.com/GenSpectrum/LAPIS/pull/642 . You should adapt the picture there too, so it is consistent.