[DOCS] Add searchable snapshots topic. (#63040) (#64319)

* [DOCS] Add searchable snapshots topic.

* [DOCS] Add definitions & remove fully-remote storage.

* [DOCS] Fixed duplicate anchor.

* Expand conceptual docs for searchable snapshots

* Rewordings

* Glossary tidy-up

* Beta

* Reword

* More performance idea to a TIP

* use -> manage

* red -> not green

* Missing space?

* Update docs/reference/glossary.asciidoc

* Fix beta label

* Use more attributes, fix link titles

* Apply suggestions from code review

Co-authored-by: debadair <[email protected]>

* Reformat

* Minor rewordings

* More minor rewordings

* Address Henning's comments

Co-authored-by: David Turner <[email protected]>
Co-authored-by: James Rodewig <[email protected]>

Co-authored-by: David Turner <[email protected]>
Co-authored-by: James Rodewig <[email protected]>