Migrate to Manifest V3

[OverPoweredDev]

Manifests V2 and below will be completely unusable from January next year. I doubt this extension uses many chrome API's that are being changed, but there's some changes to be ade to the manifest anyways.

• [ ] Naturally, changing the manifest version to "3"
• [ ] Specify host permissions separately from other permissions
• [ ] Action API unification (we don't have page actions anyways so just gotta rename)
• [ ] replace all uses of executeScript(), sendRequest() and getSelected() with the new APIs
• [ ] Change background pages to service workers (this might be a pain)

The whole list has a buncha stuff and I hopefully covered all of it

[OverPoweredDev]

Pretty sure this is Google trying to stamp out AdBlockers rather than being "part of a shift in the philosophy behind how we approach end-user security and privacy" but that's just me