Include the build output when an image build fails #1508

What happens

When GenericContainer.fromDockerfile(...).build() fails, for example because a RUN step exits non-zero, the error is:

Failed to build image

The build output is only written to the testcontainers:build debug log, so the failing step is invisible unless the run is repeated with DEBUG=testcontainers*.

Expected

The thrown error includes the failing step's output, or the last lines of the build output.

Where

• packages/testcontainers/src/container-runtime/clients/image/docker-image-client.ts sends build output to the build log only.
• packages/testcontainers/src/generic-container/generic-container-builder.ts throws Failed to build image when the image doesn't exist after the build.

Notes

• Check both the classic builder and BuildKit (withBuildkit()).
• Related: Container build logs aren't very useful because they're encoded #1049 (build logs).