Implement `/metadata` REST API endpoint
This change set implements a new /metadata REST API endpoint by
leveraging the already existing GraphQL Query.metadata.
Therefore, this endpoint is inherently on par with the GraphQL API.
This new endpoint somewhat makes the already existing /version
REST API endpoint obsolete. The reason for not just extending the
/version endpoint with the missing metadata is because the GraphQL API
also uses the metadata wording for that endpoint. I think the more
consistency the better here.
A follow up may (???) therefore properly deprecate the
/version REST API endpoint in favor of the new /metadata endpoint.
- Issue: #357032 (closed)
- Epic: &7204