Source, source type and dataset category as metadata

[aleksbobic]

Additional information about datasets provides CSX with many options to provide fine-tuned features for particular data. Users should have the option to define these when adding a new dataset.

Source: OpenAlex, Weather API, etc.
Source type: ["Uploaded", "API"] <- only these two options should be available
Dataset category: There should be a few options available ["Bibliometric", "Medical", "Survey", "News", "Social network", etc.] but users should also have the possibility to add a custom type.