[8.x] Hide progress bar on initial load when client prefers reduced m…

…otion (elastic#194365) (elastic#194496)

# Backport

This will backport the following commits from `main` to `8.x`:
- [Hide progress bar on initial load when client prefers reduced motion
(elastic#194365)](elastic#194365)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Nathan L
Smith","email":"[email protected]"},"sourceCommit":{"committedDate":"2024-09-30T14:55:49Z","message":"Hide
progress bar on initial load when client prefers reduced motion
(elastic#194365)\n\n##
Summary\r\n\r\nSee\r\nhttps://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-motion\r\n\r\n![CleanShot
2024-09-29 at 21
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progress bar on initial load when client prefers reduced motion
(elastic#194365)\n\n##
Summary\r\n\r\nSee\r\nhttps://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-motion\r\n\r\n![CleanShot
2024-09-29 at 21
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progress bar on initial load when client prefers reduced motion
(elastic#194365)\n\n##
Summary\r\n\r\nSee\r\nhttps://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-motion\r\n\r\n![CleanShot
2024-09-29 at 21
57\r\n36](https://github.com/user-attachments/assets/27436ec4-986b-4c91-9d9f-e49d59d76e7c)","sha":"2a935dcce37bd3e3f3fce32d6257b2ec7191dac5"}}]}]
BACKPORT-->

Co-authored-by: Nathan L Smith <[email protected]>

packages/core/apps/core-apps-server-internal/assets/legacy_styles.css

@@ -114,3 +114,9 @@ body, html {
     transform: scaleX(1) translateX(100%);
   }
 }
+
+@media (prefers-reduced-motion) {
+  .kbnProgress {
+    display: none;
+  }
+}