Docs: Add Callout to Stacks Helper page about limited flexbox gap sup…

…port (#34910)

* Docs: Add Callout to Stacks Helper page about limited flexbox gap support

Fixes: #34737

* Update stacks.md

* Delete callout-warning-flexbox-gap.md

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

site/content/docs/5.1/helpers/stacks.md

@@ -8,6 +8,10 @@ toc: true
 
 Stacks offer a shortcut for applying a number of flexbox properties to quickly and easily create layouts in Bootstrap. All credit for the concept and implementation goes to the open source [Pylon project](https://almonk.github.io/pylon/).
 
+{{< callout warning >}}
+Heads up! Support for gap utilities with flexbox was recently added to Safari, so consider verifying your intended browser support. Grid layout should have no issues. [Read more](https://caniuse.com/flexbox-gap).
+{{< /callout >}}
+
 ## Vertical
 
 Use `.vstack` to create vertical layouts. Stacked items are full-width by default. Use `.gap-*` utilities to add space between items.