feat: use atlas in make pull_translations

Changes
-------
 - Bump frontend-platform to bring `intl-imports.js` script
 - Move all i18n imports into `src/i18n/index.js` so `intl-imports.js` can
   override it with latest translations
 - Add `atlas` into `make pull_translations` when `OPENEDX_ATLAS_PULL`
   environment variable is set.

Refs: [FC-0012 project](https://openedx.atlassian.net/l/cp/XGS0iCcQ) implementing Translation Infrastructure OEP-58.