DDLS-444 add linting to github actions

[jamesrwarren]

Purpose

Add linting to our Dockerfiles

Fixes DDLS-444

Approach

Decided to use hadolint as it's a popular tool and can be used securely. It has a github action but I actually like just using the docker container for a few reasons.

Firstly it's really easy to programmatically get all our dockerfiles in the repo and chevron them through to the docker container. We can also mount the single file for the config.
Secondly I like that it shows how you can recreate the issues locally by using the same command.
Finally as an edge case it's more secure, as a docker image that was compromised still doesn't have access to env vars or the filesystem and we simply push particular files into it at run time. An action on the other hand has a wider scope of things it can do with regards to the file system.

I've fixed most things. I've set a few to ignore. In particular I'm ignoring pinning of certain packages we specify in the dockerfile as I don't think renovate will handle updates for them and we deploy based on fixed images so if something were to break it wouldn't make it to prod and it means we're always up to date with the docker 'os' (so to speak). Will revisit my thinking around this but this is what I've gone for for now.

Learning

NA

Checklist

• I have performed a self-review of my own code
• I have updated documentation (Confluence/ADR/tech debt doc) where relevant
• I have added tests to prove my work
• The product team have approved these changes
• I have checked my work for potential security issues and refered to the OWASP top 10

Frontend

• I have run an in-browser accessibility test (e.g. WAVE, Lighthouse)
• There are no deprecated CSS classes noted in the profiler
• Translations are used and the profiler doesn't identify any missing
• Any links or buttons added are screen reader friendly and contextually complete
• If adding GA events, I have updated or checked the existing category or label values