[Task]: Migrate all projects from `yarn` to `npm`

[willdurand]

Description

We've historically used both, switching to yarn when npm was no longer the cool kid. It looks like npm has been solid for a number of years now, and we are likely still using yarn v1, which means we don't need any of the yarn features. Let's switch all the yarn-projects to npm.

Acceptance Criteria

• addons-blog
• extension-workshop
• addons-frontend
• ...

┆Issue is synchronized with this Jira Task