Make generated JSON Schema available in PR

[albertmink]

• upload generated JSON Schema in GitHub Action
• improve readability in error scenario by creating annotations

[larshp]

alternatively/supplement by adding it as an artifact to the run

https://github.com/actions/upload-artifact

[albertmink]

yeahh, upload does zip the content. This means, you want to see the content, then download, unzip, open with editor. For me this is too much, if you only are interested in having a glimpse.
I'm still not sure what to do with the generated schema. But as they are generated anyhow, it felt intuitive to make the result somehow available. Somehow -> just paste in the GitHub Action logs.

/// edit
Size of the entire log of the JSON Schema generation Action is around 500 KB (10000Lines). So, file size should not be a problem.