Migrate to Manifest v3

[luciomartinez]

There's no ETA for when v2 will be deprecated but it'll likely happen soon. Chrome and Firefox have two implementation so each of their guidelines needs to be reviewed.

• Chrome guide: https://developer.chrome.com/docs/extensions/mv3/intro/mv3-migration/
• Firefox guide: https://blog.mozilla.org/addons/2021/05/27/manifest-v3-update/