[FEATURE] Add filtering options to document retrieval

[eriknovak]

Is your feature request related to a problem? Please describe.
Providing documents based on the user query is nice, but it would be beneficial to provide some filtering options.

Describe the solution you'd like
The option to filter the results of the user query based on:

• environmental tags
• NUTS tags
• named entities

These filtering parameters should be optional and should be added to the query (e.g.
/route?text=some text&nuts=dw1,dw3&env_tags=deforestation)