- Use JS regex for emoji validation
- Add test for blocking emojis in full name
- Fix existing tests for user status that failed locally

The private commit email is automatically generated in the format:
id-username@noreply.HOSTNAME

GitLab instance admins are able to change the HOSTNAME portion,
that defaults to Gitlab's hostname, to whatever they prefer.

Since the frontend for this feature isn't ready, better to hide the
confusing field behind a feature flag.

This can be done trough the API for the current user, or on the
profile page.

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

If using gravatar.com, both plain_url and ssl_url in settings are now
served via HTTPS. Make this the default.

[ci skip]

Closes #20918

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

See merge request !2071

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