[monorepo] Use a locally installed prettier version

Summary:
Currently users must globally install prettier and eslint for arc lint to work. This creates issues as in practice it is easy to globally install a different version of prettier, or for the globally installed version to vary with different versions of nodejs.

Pin the version by getting the bin from top-level node_modules.

This seems overkill for "just prettier." Plan is to extend this to eslint and also mocha / jest so that arc unit can work (only on repos that were impacted by any given diff).

Test Plan: arc lint --everything

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D17413