Proposed changes

Adds a workflow which can force the latest SHAs for images pinned in build/Dockerfile and tests/Dockerfile. This opens a PR against the branch that it targets, so should work for main or release-* branches. Also supports excluding images that match a given pattern.

Sample PR (Note: branch name is incorrect as it was triggered from a push, branch name will normally be chore/image-update-<source branch>-<dockerfiles hash>)

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork