Migrating to the Manifest v3

[Matsuuu]

The extension was written with Manifest v2 since that was the one that had guides and docs nicely laid out.

Migrating to Manifest v3 shouldn't be too much of a re-design (as per https://developer.chrome.com/docs/extensions/mv3/intro/mv3-migration/) but the background pages moving to service workers might prove an issue with how Nydus works currently and needs to be tested around.

https://developer.chrome.com/docs/extensions/mv3/migrating_to_service_workers/