CLOUDP-286235: Improved tooling (ESLint/Prettier) and GH actions

[lovisaberggren]

Proposed changes

• Moving package.json to root for sharing between tools
• Added Prettier and ESLint
• Added GH workflow step for Prettier and ESLint

Jira ticket: CLOUDP-286235

Running locally:

# Reformat with Prettier
npm run format

# Run Prettier check (no reformat)
npm run format-check

# Run ESLint check (JS files)
npm run lint-js

Further comments

We can consider running the existing spectral linting with the package.json instead of a makefile (planned approach for new ipa validator)

[gssbzn]

can be done as a follow up but let's make sure dependabot tracks this file

[gssbzn]

rather than retry can you enable cache for setup node https://github.com/actions/setup-node?tab=readme-ov-file#caching-global-packages-data

[lovisaberggren]

Done, also updated the same on the req spec validations workflow 👍