feat: rework validation logic to return errors as strings

[ReneSchroederLJ]

Description

• refactored validation for Demand, Production, Delivery and Stock to return detailed error messages
• the data import API now returns the detailed errors
• refined swagger annotations for data import

resolves #906

Pre-review checks

Please ensure to do as many of the following checks as possible, before asking for committer review:

• DEPENDENCIES are up-to-date. Dash license tool. Committers can open IP issues for restricted libs.
• Copyright and license header are present on all affected files
• If helm chart has been changed, the chart version has been bumped to either next major, minor or patch level (compared to released chart).

[tom-rm-meyer-ISST]

Great enhancements! I tracked the changes in this comment also within 906. (small things open).

I noticed the following:

• a few validations missing (also previously in the validate method) like order positions or address cross check
• semantics to be improved in the error message
• harmonization of . at the end of the message (this was wrong in two services, resulting in the majority of the comments)

I used the attached files for easer tracking with no int seed.
delivery.xlsx
demand.xlsx
production_no_fail.xlsx
stock_soft_fail.xlsx

[tom-rm-meyer-ISST]

Thanks for the fast improvements!

Found a feww smaller things to consider.

[tom-rm-meyer-ISST]

Thanks a lot for iterating over this topic with me! Great feature!