Make use of EWE's experimental allowlisting API for websites

Background / User story

We'd like to experiment with giving websites a way to ask users to allowlist them to provide a better user experience than we can currently offer via the extension's own UI. Since this is just an experiment at this point, the API should be restricted to trusted partners.

Therefore we should make use of EWE's newly introduced allowlisting API (see eyeo/adblockplus/abc/webext-sdk#171 (closed)).

What to change

• Design: N/A
• Research: N/A
• Spec: N/A
• Legal: N/A
• Development:
  • Pass list of authorized keys to EWE via allowlisting.setAuthorizedKeys().
  • Pass function to EWE via allowlisting.setAllowlistingCallback() that allowlists a domain the same way as the "filters.allowlist" message.

Hints for testers

• This change was merged into the feature-8 branch.
• Allowlisting the domain or just the URL via the icon popup toggles should continue working as expected.
• See hints for testers in #1114.

Hints for translators

N/A