**Goal**
Create a top-level search section. This will let us clean up our search
API reference docs, particularly content from [`Request body search`][0].
**Changes**
* Creates a top-level `Search your data` page. This page is designed to
house concept and tutorial docs related to search.
* Creates a `Run a search` page under `Search your data`. For now, This
contains a basic search tutorial. The goal is to add content from
[`Request body search`][0] to this in the future.
* Relocates `Long-running searches` and `Search across clusters` under
`Search your data`. Increments several headings in that content.
* Reorders the top-level TOC to move `Search your data` higher. Also
moves the `Query DSL`, `EQL`, and `SQL access` chapters immediately
after.
Relates to #48194
[0]: https://www.elastic.co/guide/en/elasticsearch/reference/master/search-request-body.html
James Rodewig