[Saved Search] Update saved search schema to allow empty sort arrays (

elastic#156769)

## Summary

This PR removes the `minSize` restriction added in elastic#154016 from the
saved search schema `sort` property, which was causing AWS integrations
to fail.

Before:

![broken](https://user-images.githubusercontent.com/25592674/236355150-112e103b-00ef-4f0d-baa5-35de6b944152.gif)

After:

![working](https://user-images.githubusercontent.com/25592674/236355167-1185279b-84ef-4570-8762-90944c839c4d.gif)

Fixes elastic#156724.

### Checklist

- [ ] ~Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)~
- [ ]
~[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials~
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] ~Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard
accessibility](https://webaim.org/techniques/keyboard/))~
- [ ] ~Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))~
- [ ] ~If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)~
- [ ] ~This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))~
- [ ] ~This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)~

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

(cherry picked from commit 2f53207)

src/plugins/saved_search/server/saved_objects/search.ts

@@ -53,8 +53,8 @@ export function getSavedSearchObjectType(
         columns: schema.arrayOf(schema.string(), { defaultValue: [] }),
         sort: schema.oneOf(
           [
-            schema.arrayOf(schema.arrayOf(schema.string(), { minSize: 2, maxSize: 2 })),
-            schema.arrayOf(schema.string(), { minSize: 2, maxSize: 2 }),
+            schema.arrayOf(schema.arrayOf(schema.string(), { maxSize: 2 })),
+            schema.arrayOf(schema.string(), { maxSize: 2 }),
           ],
           { defaultValue: [] }
         ),