Unauthenticated super sidebar

What does this MR do and why?

Update Super Sidebar to support logged out users

This changes the Super Sidebar to support a logged-out state:

1. Removes all User related items from the sidebar (profile links, and create menu, pinned items)
2. Removes the Brand Logo, Next badge as well, because those will be shown in the header banner which is being added as part of: #389603 (closed)
3. Removes the context switcher. It is going to be moved for logged in users as well: #409522 (closed)

On the backend side the super_sidebar_context has been split into two methods, one for anonymous, the other for logged-in users.

A changelog entry isn't warranted, because this feature is currently not reachable.

New feature flag for logged-out super sidebar

This feature flag is being introduced to control whether logged-out users see the super-sidebar or not.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. echo "Feature.enable(:super_sidebar_logged_out)" | rails c
2. In an igcognito window (or logged out) go to any public GitLab route e.g. /flightjs/Flight/-/merge_requests/4

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #389603 (closed)