Feature/improve ci

[GCHQDeveloper581]

Description
Some performance/usability/security improvements to the pull_request workflow script

• Use 'npm ci' rather than 'npm install' to prevent updates being pulled in when doing the CI run/build
  • prevents package-lock.json being modified mid-build
  • increases consistency of builds
  • reduces the risk of unintentionally pulling in malicious updates
• move UI tests before production image build
  • UI tests don't require the docker image(s), and doing the testing first reduces the time till testing is complete and hence time-to-failure in the event of a bad tree
• save artefact from build
  • allows the built code to be tested locally without having to do a local build

AI disclosure
No use of AI

Test Coverage
N/A