feat(alert): add htmlAttributes property for passing attributes to buttons (#27862)

Issue number: N/A

---------

## What is the current behavior?
Buttons containing only icons are not accessible as there is no way to
pass an `aria-label` attribute (or any other html attribute).

## What is the new behavior?
- Adds the `htmlAttributes` property on the `AlertButton` interface 
- Passes the `htmlAttributes` to the buttons
- Adds a test to verify `aria-label` and `aria-labelled-by` are passed
to the button

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

core/src/components/alert/alert-interface.ts

@@ -48,6 +48,7 @@ export interface AlertButton {
   role?: 'cancel' | 'destructive' | string;
   cssClass?: string | string[];
   id?: string;
+  htmlAttributes?: { [key: string]: any };
   // TODO(FW-2832): type
   handler?: (value: any) => AlertButtonOverlayHandler | Promise<AlertButtonOverlayHandler>;
 }