[Bug] Update extension manifest to v3

[vidorteg]

🐞 Bug report

Description

Webhint extension requires it manifest to be update to version 3:

Details

Manifest V2 is on the process on being deprectated, on January 2023 extension using v2 will not be able to be updated so this extensions needs to be migrated to v3.
https://developer.chrome.com/docs/extensions/mv3/mv2-sunset/

[vrishtrix]

Creating a PR to bump the manifest version to v3