Implement a cookie banner

[Iinh]

We have received guidance from our legal team that we need to include a cookie banner on all Mozilla websites that use cookies (beyond strictly necessary cookies) and/or analytics in order to be transparent to our users and to reduce our exposure to legal risks from changes in EU and US privacy law over the last several years.

Also see: https://mozilla-hub.atlassian.net/wiki/spaces/EN/pages/538050566/Cookie+Banner+Implementation+On+Mozilla.org