Whenever we already deal with a User object, let's use the more specific
method avatar_icon_for_user.

Add CHANGELOG entry

Instead of the JS being in charge of the HTML, the HAML now handles it.
The HAML can then check the cookie & show it needed. It also allows the
HAML access to the paths so we don't have to pass that through.

Closes #29955

Closes #28842

Adds rel="noopener noreferrer" to all links with target="_blank"

See merge request !2071

Now it appends a template instead of relying in a partial
to show it.

Also changed the cookie sets to true and false values to make
it consistent with the rest of the javascript.

Fixed some haml and a missing new line

Also improved accesibility and change the id from user_callouts to a class

Also changed the user_callout haml to a partial and
added the corresponding SVG icon

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>