Add image source label to dockerfiles

[wuast94]

To get changelogs shown with Renovate a docker container has to add the source label described in the OCI Image Format Specification.

For reference: https://github.com/renovatebot/renovate/blob/main/lib/modules/datasource/docker/readme.md

• [ ] commit message named according to Contributing Guide
• [x] npm run fix:lint is OK
• [x] npm test is OK