Add rippled-tools image containing Prettier for file formatting

[bthomee]

To avoid having to set up Node.JS, NPM, and install Prettier from scratch each time, this PR creates a new tools-rippled-prettier image with everything already configured.

See XRPLF/rippled#5665 for where it will be used.

[Bronek]

Any chance you could do this with pnpm ? Asking because I think that's the only NPM package manager supporting lockfiles, and a lockfile seem an important security feature, given that NPM has pretty poor security by itself. For reference:

• Understanding the Difference Between package.json and pnpm-lock.yaml in Node.js
• The PNPM Lockfile
• pnpm install reference
• prettier install with pnpm - note, you would have to use pnpm i --frozen-lockfile to enforce lockfile (I think)
• pnpm installation instruction

[mvadari]

npm also supports lockfiles

[bthomee]

I propose doing more rigorous locking in a follow-up PR, if at all, especially since this Docker image will only be used to run on PR commits but not on PR merges.