[lib] Use Webpack 5 asset/inline instead of deprecated url-loader

Summary:
See docs here and deprecation notice here.

Depends on D6701

Test Plan: I tested dev build in landing and web (we only use this plugin in dev builds) via yarn dev in landing + web + keyserver and then tested the website

Reviewers: atul, tomek

Reviewed By: atul

Differential Revision: https://phab.comm.dev/D6702