feat(error): handle 422 errors from the API

[EtienneM]

Here is the output:

 blscalingo --app biniou env-set PORT=12345
 !     422 Unprocessable Content
* PORT → Name is reserved

Fix #1155

• Add a changelog entry in the section "To Be Released" of CHANGELOG.md

[EtienneM]

Removed rootCause that is useless with go-utils/errors/v3. I should have adapted this code in #1196

[briceamen]

Very clean, LGTM