1644: Add validation to importAcceptingStores mutation in the backend

[seluianova]

Short Description

Currently we have csv validation on the administration side, but no validation on the backend.
This means that if the request is sent directly to the backend, our validation rules can be violated.

Proposed Changes

• remove import pipeline for nuernberg
• add validation that the mandatory fields are not empty (name, street, houseNumber, postalCode, location)
• return an error, if request contains duplicates (consider records as duplicate if the name, street, house number, zip code, and location are the same)
• add data cleaning (remove trailing whitespaces)

Not included:
Check that the categoryId refers to the current project.
I think it would be better to do it after #1915 ❓

Side Effects

no?

Testing

tbd

Resolved Issues

Fixes: #1644