ci: add swagger editor validate

[ariwk]

Proposed changes

Due to problems in OpenAPI specifications automated checks must be implemented #279

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation

[ariwk]

Hi @SchweizerischeBundesbahnen/sbb-clew-polarion-maintainers
we need to first fix the problems in the spec before merging ;-)
Till now the workflow works and identifies problems
Cheers, Adam

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud