This change adds a new `kibana_admin` role, and deprecates
the old `kibana_user` and`kibana_dashboard_only_user`roles.
The deprecation is implemented via a new reserved metadata
attribute, which can be consumed from the API and also triggers
deprecation logging when used (by a user authenticating to
Elasticsearch).
Some docs have been updated to avoid references to these
deprecated roles.
Co-authored-by: Tim Vernum <tim@adjective.org>
Co-authored-by: Larry Gregory <legrego@users.noreply.github.com>