Add SNYK scan to build image

[RMcVelia]

Context

We should scan the build image using SNYK

Changes proposed in this pull request

• Update the build workflow to use our build-docker-image github action, and add SNYK key so it runs the scan.
• Add weekly build without caching workflow

Guidance to review

Check build log: https://github.com/DFE-Digital/access-your-teaching-qualifications/actions/runs/12651587377

build-no-cache: https://github.com/DFE-Digital/access-your-teaching-qualifications/actions/runs/12651449855

Link to Trello card

https://trello.com/c/9tIfEgW1/2166-scan-docker-image-in-all-repositories

Checklist

• Attach to Trello card
• Rebased main
• Cleaned commit history
• Tested by running locally

[github-actions]

Deployments

App	URL
Access Your Teaching Qualifications	https://access-your-teaching-qualifications-pr-926.test.teacherservices.cloud
Check A Teacher's Record	https://check-a-teachers-record-pr-926.test.teacherservices.cloud

[saliceti]

Can we remove the existing action? https://github.com/DFE-Digital/access-your-teaching-qualifications/tree/main/.github/actions/build-image