Allow filtering discussions for anonymous users

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Close this issue

With https://gitlab.com/gitlab-org/gitlab-ce/issues/26723 we introduce filtering discussion capabilities for issues and merge requests, but this is only available for logged in users. We should also make this available for anonymous users.

A compelling use case for this is, for example, opening an issue on your phone (without being logged in) and wanting to just follow the comments.

A possible approach to this is saving the filter option to a cookie or local storage. Like https://gitlab.com/gitlab-org/gitlab-ce/issues/2672, the option should be saved instance-wide bu separately for issues and for merge requests.