Previously, cross-cluster replication (CCR) documentation was located in
the Stack Overview:
https://www.elastic.co/guide/en/elastic-stack-overview/master/xpack-ccr.html
This adds CCR documentation to the Elasticsearch Reference Guide with a
level offset for headings.
The level offset and CCR Stack Overview docs will be removed in later
commits.
This is related to #35975. It adds documentation on the remote recovery
process. Additionally, it adds documentation about the various settings
that can impact the process.
This commit is our first introduction to cross-cluster replication
docs. In this commit, we introduce the cross-cluster replication API
docs. We also add skelton docs for additional content that will be added
in a series of follow-up commits.