[DOC] Server UUID Setting (elastic#128399) (elastic#131177)

The `server.uuid` setting MUST be a valid UUIDv4.
Also, the setting was added in the middle of other SSL settings and it was misleading (due to a banner related to SSL settings).

(cherry picked from commit 9a34c20)

Co-authored-by: Luca Belluccini <[email protected]>

Author: kibanamachine

docs/setup/settings.asciidoc

@@ -608,6 +608,9 @@ all http requests to https over the port configured as <<server-port, `server.po
  | An array of supported protocols with versions.
 Valid protocols: `TLSv1`, `TLSv1.1`, `TLSv1.2`, `TLSv1.3`. *Default: TLSv1.1, TLSv1.2, TLSv1.3*
 
+|[[server-uuid]] `server.uuid:`
+ | The unique identifier for this {kib} instance. It must be a valid UUIDv4. It gets automatically generated on the first startup if not specified and persisted in the `data` path.
+
 | [[settings-xsrf-allowlist]] `server.xsrf.allowlist:`
  | It is not recommended to disable protections for
 arbitrary API endpoints. Instead, supply the `kbn-xsrf` header.