Introduce `stemcell` block under releases
Introduce `stemcell` block under releases

This was introduced with [cli v2.0.30](https://github.com/cloudfoundry/bosh-cli/releases/tag/v2.0.30).

Co-authored-by: Max Becker <e6d855fe2263fd0035edb7e1f665a7466a1b4c9c@sap.com>
cloudfoundry/docs-bosh