Filter in headers is not parsed to comply with mongo syntax

Issue Name

Filter in headers is not parsed to comply with mongo syntax

Summary

When passing a filter in a request header, if the filter has mongo-specific syntax, the request fails

Steps to Reproduce

curl -X GET --header 'Accept: application/json' --header 'Filter: {"where":{"sourceFolder":{"inq":["something"]}},"fields": {"pid":1,"size":1,"sourceFolder":1}}' 'http://localhost:3000/api/v3/Datasets'

Current Behaviour

the command above returns 500, because the "inq" in the filter is not converted to "$in" required by mongo (while it correctly happens if the filter is set as a query param)

Expected Behaviour

should return 200 having applied the filter

Extra Details

One solution could be this, but in general, it might make sense to add a middleware (e.g. here) acting on all requests which, in case there is a filter in the headers, it adds it as a query parameter.

Start by reproducing the curl request against the Datasets endpoint, then inspect src/datasets/datasets.controller.ts around lines 110-112 and the common middleware entry point suggested in the issue. Compare header and query-parameter filter handling. Done means the shown Mongo-style header filter returns 200 and is applied correctly.