Shrink docker image from 1.64GB -> 740MB

[rmlearney-digicatapult]

Pull Request

Checklist

• Have you read Digital Catapult's Code of Conduct?
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

PR Type

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• Chore

Linked tickets

High level description

Change docker build process and underlying image to shrink final production image to 734MB

Detailed description

Rebased final image on node:lts-bookworm-slim with curl and openssl installed and cache cleaned
Using dive discovered that npm prune --omit=dev leaves a lot of unnecessary cache, so moved this to separate build stage and copied node_modules into final production image

Some other minor changes

This is nearing the theoretical limit for a docker image size for this project:
node 120MB
node_modules 448MB
/www 2MB

Describe alternatives you've considered

Operational impact

Additional context

[rmlearney-digicatapult]

It is possible to reduce the image size further to 660MB by using RedHat UBI9-minimal as the base image for the production layer, but I reverted these changes because it's not a distro we've used before.