Detect images to be built automatically

[henninggross]

Previously the images to be built via build-and-push-images.sh were determined via this line in the script itself:

IMAGES="buildah finish go-toolset gradle-toolset helm sonar start webhook-interceptor python-toolset"

As this is a hardcoded list it could happen (as it did with Typescript) that new images are added as a Dockerfile that are not added to this list.

With this change the script now iterates over the contents of /build/package/ and retrieves the images to be built from this, which should not lead to missing images anymore.

Fixes #286

Tasks:

• Updated design documents in docs/design directory or not applicable
• Updated user-facing documentation in docs directory or not applicable
• Ran tests (e.g. make test) or not applicable
• Updated changelog or not applicable

[michaelsauter]

Nice!