Allow danger to run with dependencies

What does this MR do?

I am working on adding reviewer roulette to danger-bot in danger-bot!18 (merged). This requires changing the danger-bot job to support new dependencies. I decided to create a new image since vendoring the dependencies felt awful.

This change should be backwards compatible. I created images for the old versions by writing Dockerfile.backport:

FROM registry.gitlab.com/gitlab-org/gitlab-build-images:danger

COPY . /danger/

and then running this script:

#!/bin/bash

for tag in $(git tag --list); do
  git checkout "$tag"
  docker build -t "registry.gitlab.com/gitlab-org/security-products/danger-bot:${tag}" -f Dockerfile.backport .
  docker push "registry.gitlab.com/gitlab-org/security-products/danger-bot:${tag}"
done

Versions 0.0.1 - 0.0.6 all have published docker images.

You can see the results of testing this job at gitlab-org/security-products/analyzers/cluster-image-scanning!4 (closed)

I also tested that this works on v0.0.6 at gitlab-org/security-products/analyzers/cluster-image-scanning!5 (closed)

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug