Replacement Image Processing Tasks Needed after Imagemin Removal from Gulp Tasks

[jeremy-farrance]

After moving imagemin and its 2 plugins from our devDependencies (see pull 36), we need to add back these features in some modern and maintainable way.

Current intention and idea is to do them with Webpack in this old Bs4 template. Though in Tw4 we will probably instead be doing it via Rollup (or Vite or Rolldown or ??).