Shrink Docker image size by ~1/3 by removing unnecessary ops

[thespad]

Current image does two very inefficient operations:

• It copies node_modules from shared-libs-builder stage to backend-builder stage and then in the runner stage copies node_modules from both stages again, even though the backend-builder stage now contains all the necessary modules.
• It chowns the whole of /app after COPYing the files from previous stages

Both of these result in duplicating all of the affected files in the runner stage layers, which gives you about 600Mb of wasted space.

By removing the duplicate COPY of node_modules, and performing the chown as part of the COPY operation, that space can be free, reducing the image size substantially.

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[brendan-kellam]

Thanks for the PR this is really great!! Heads up, I was hitting the following error when building locally:

ERROR: failed to solve: invalid chmod parameter: '+x'. it should be octal string and between 0 and 07777

It's probably because whatever bundled Dockerfile syntax version on my machine is less than version 1.14.0 where they introduced non-octal chmod params.

I think it would be best to add # syntax=docker/dockerfile:1 to the top of the Dockerfile such that we use the latest Dockerfile syntax. (docs)

[thespad]

Done. It's what I'd normally do when building a Dockerfile from scratch but I try not to assume too much when modifying other peoples' work.

[brendan-kellam]

thank you for this PR, it's super helpful!