* Remove `es-test-dir` book-scoped variable
* Remove `plugins-examples-dir` book-scoped variable
* Remove `:dependencies-dir:` and `:xes-repo-dir:` book-scoped variables
- In `index.asciidoc`, two variables (`:dependencies-dir:` and `:xes-repo-dir:`) were removed.
- In `sql/index.asciidoc`, the `:sql-tests:` path was updated to fuller path
- In `esql/index.asciidoc`, the `:esql-tests:` path was updated idem
* Replace `es-repo-dir` with `es-ref-dir`
* Move `:include-xpack: true` to few files that use it, remove from index.asciidoc
This PR extends the basic Prevalidation API so that in case there are
red non-searchable-snapshot indices in the cluster, we reach out to
the nodes (whose removal is being prevalidated) to find out if they
have a local copy of any red indices.
Closes#87776
This PR adds the first part of the Prevalidate Node Removal API. This
API allows checking whether attempting to remove some node(s) from the
cluster is likely to succeed or not. This check is useful when a node
needs to be removed from a RED cluster, without risking loosing the last
copy of some RED shards.
In this PR, we only check whether a RED index is a Searchable Snapshot
index or not, in which case the removal of any node is safe as the RED
index is backed by a snapshot.
Relates #87776
