Improvements for Problem guideline

[ktsypkina]

Incorporate API Guild thoughts on detailing Problem Object guidelines (#763)

[zalando-compr-opensource]

invalid team ID

The team ID in your .zappr.yaml file does not appear to be valid. Please, fix
this before team ID checks will be added back into ComPR's specification check.

You can follow this guideline for help.

[tfrauenstein]

Thank you. I like the guideline improvement -- provides more details and clarity. However, I think we should avoid redundant and inconsistent change of the Problem Object specification -- see my comment.

[tfrauenstein]

I think we should avoid specification of the problem object in the GUI guideline redundantly (and possibly inconsistently) to the open-source specification in https://opensource.zalando.com/restful-api-guidelines/models/problem-1.0.1.yaml

Instead we should clearly refer to it and update it as part of the PR, if helpful.
It also allows us to better understand the differences.

[ePaul]

I agree that we should avoid redundancies, but having it written out in the guidelines makes it easier to read than just pointing to the file. Not sure what the best way of doing this is, though.