This change reintroduces the system index APIs for Kibana without the
changes made for marking what system indices could be accessed using
these APIs. In essence, this is a partial revert of #53912. The changes
for marking what system indices should be allowed access will be
handled in a separate change.
The APIs introduced here are wrapped versions of the existing REST
endpoints. A new setting is also introduced since the Kibana system
indices' names are allowed to be changed by a user in case multiple
instances of Kibana use the same instance of Elasticsearch.
Relates #52385
Backport of #54858
3600c9862f