Spam fighting: please allow to use akismet on bio and website_url of users

On https://framagit.org, the main spam problem is not issue spamming but spam in bio and website_url of users.

It would really great to have Akismet check on those fields when users modify them.

Design proposal

• a checkbox in /admin/application_settings/reporting to enable akismet on bio and website_url + field for akismet API key + checkbox "use same API key than for issues check". I want to split akismet checks for issues and for bio to avoid make too much API calls to Akismet (since we don’t have spam problems on issues, we don’t need to check them)
• generate an abuse report when users fill a bio/website_url detected as spam by Akismet. A button would allow to declare the bio as false positive (which would trigger a false positive declaration API call to Akismet)
• on admin page of users (/admin/users/username), there would be a button to report the bio/website_url as spam to Akismet