set-output has been deprecated: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

- use 1.4 syntax to support `COPY --link` commands
- set NODE_ENV=production
- remove $WORK build arg

…ching

- If e.g. `test` has been added in a command/step, removing it in a
subsequent command/step does not have a positive effect on the image size.
Rather, we add it .dockerignore to stop adding it in the first place.
- node_modules/.cache & /tmp/Relay* are populated by Webpack plugins.

app/server.js reads .entrypoints.main.assets in order to generate an appropriate
manifest and `preload` tags, but it doesn't need the rest. This is why we turn
all stats off via `all: false` and then selectively turn `entrypoints` on.

Before, stats.json was 82mb, now it is ~9kb.

Even if a commit has changed `yarn.lock`, we can use an old `.yarn/cache` directory, so that we don't have to fetch 99% of all dependencies again.

…ction

This reverts 32bbfa8, which reverts 3f6e105, which apparently failed because of an unrelated problem[1].

[1] https://github.com/HSLdevcom/digitransit-ui/actions/runs/4762670497/jobs/8469259999

This probably improves favicons-webpack-plugin's performance, as node_modules won't be resolved for resolving the path.

This speeds up the webpack build within the Docker image build significantly.

Co-Authored-By: Jannis R <[email protected]>

…github actions

cherry-pick of b8333bd