Changes:
* Renames 'full copy searchable snapshot' to 'fully mounted index.'
* Renames 'shared cache searchable snapshot' to 'partially mounted index.'
* Removes some unneeded cache setup instructions for the frozen tier. We added a default cache size with #71844.
In #71701 we added a new REST API that provides statistics
about the searchable snapshots cache on Frozen Tier.
This commit adds the necessary plumbing to expose this API
in the High Level REST Client. It also exposes the documentation
of the Mount Snapshot API that was created in #68949 but not
made accessible.
James Rodewig
Tanguy Leroux
Jason Tedor