Host permission requirement

To redirect requests, the extension needs host permissions.
While "Manage Extensions" (about:addons) offers a built-in UI to grant or revoke permissions, this extension uses the permissions API to build the request into the UI:

Allow access to example.com

Test cases

There are four rules in redirect-rules.json; each rule has a test case here.

1: example.com/ should redirect to redirectTarget.html packaged in the extension.
2: example.com/ew should redirect to extensionworkshop.com
3: https://www.example.com/anything should redirect to https://example.com/anything?redirected_from_www=1.
4: http://example.com/no_question should redirect to https://example.com/no_question?redirected_by_regex.