* 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
Changes:
* Adds a tutorial for search templates.
* Adds reference docs for the render search template API.
* Improves parameter documentation for the multi search template API.
* Removes duplicate examples from the search template API, multi search API, and create stored script API docs.
* Splits the source files for the search template API and the multi search template API docs.