Add default “npm run build” for project (with docs updates)

[colinrotherham]

Our tasks.md docs talk about serving the review app directly with:

npm run serve --workspace govuk-frontend-review

But we didn't explain that an MVB™ (minimum viable build 😆) was needed first:

• build GOV.UK Frontend using npm run build:package
• build Rollup stats YAML using npm run build:stats in #3681
• build Express.js "Review app" using npm run build:app

This PR adds a convenient npm run build script to solve this problem and was split out from:

• Add Rollup stats to review app #3681

[colinrotherham]

Our default build is to prepare the review app for launch

1. Build govuk-frontend package
2. Build govuk-frontend-review assets

But notice that the webpack example isn't included? For GitHub Actions Tests we instead run:

govuk-frontend/.github/workflows/actions/build/action.yml

Line 23 in 0116919

run: npm run build --workspaces --if-present

By adding a new npm run build we can run it before key scripts

E.g. Ensuring we have the govuk-frontend package built before we import it

[romaricpascal]

suggestion Would it be worth invoking build:app and build:package here via concurrently rather than use npm to limit risks of the commands diverging if we update them?

[colinrotherham]

@romaricpascal Ah we can't I'm afraid, review app relies on govuk-frontend/dist/** things

Any thoughts on using npm run build (default) versus npm run build:package (named)?

[colinrotherham]

Let's narrow it down when we add the stats package (also needs pre-building) in:

• Add Rollup stats to review app #3681

[romaricpascal]

Looks good, especially in anticipation of building the stats. Just a little suggestion to reuse the existing tasks for avoiding future divergence, but I'm fine if it goes as is 😊

[romaricpascal]

suggestion Would it be worth invoking build:app and build:package here via concurrently rather than use npm to limit risks of the commands diverging if we update them?