broken without undocumented HADOLINT_DOCKERFILE variable

Thanks. This is great.
I have this running but here is some observations:

I am wanting to have a pipeline that lints a Dockerfile and then builds it.

• By default this will run in the test stage which is AFTER a build
• This will not run unless you set HADOLINT_DOCKERFILE as a variable

Please consider setting a default for HADOLINT_DOCKERFILE but allow it to be overridden.

---

default:
  tags:
    - platformtest

stages:
  - lint
  - build
  - test

variables:
  HADOLINT_DOCKERFILE: 'Dockerfile'

include:
  - component: $CI_SERVER_FQDN/guided-explorations/ci-components/hadolint/hadolint@0.1.4
    inputs:
      stage: lint
  - component: $CI_SERVER_FQDN/guided-explorations/ci-components/kaniko/kaniko@2.2.2
    inputs:
      KANIKO_REGISTRIES: 'gitlab'