Dependency/vulnerability scanning check on PR and merge

[jeff-horton-ho-sas]

• [ ] Use SAS-Github actions to run Trivy on Docker images created in build
• [ ] Add NPM audit to PR checks to catch issues early
• [ ] Delete Snyk webhook once above actions complete

[jeff-horton-ho-sas]

https://github.com/UKHomeOffice/sas-github-workflows/blob/main/.github/actions/trivy-image-scan/action.yml