Simplify datasetparameters retrieval

Once this is merged icat-plus!693 (merged), it will be possible to get the unique values of multiple dataset parameters in one go.

So, this:

https://icatplus.esrf.fr/catalogue/datasetparameter?unique=true&investigationId=1577150098&name=scanType&datasetType=acquisition

can be replaced by:

http://localhost:8000/catalogue/---/datasetparameter/values/investigationId=1577150098&name=scanType&datasetType=acquisition

Besides, multiple parameters (like the ones used in summary) can be used too:

http://localhost:8000/catalogue/--datasetparameter/values?investigationId=1577150098&name=scanType,SampleTrackingContainer_id&datasetType=acquisition