feat(header): add new divider property (#29675)

Issue number: internal

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## What is the new behavior?
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this PR. -->

- Add new divider property on header's Ionic theme
- Added new divider test.
- Added TODO for support on ios/ md in future.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

[Header divider
sample](https://ionic-framework-a13vvxiyy-ionic1.vercel.app/src/components/header/test/divider?ionic:theme=ionic)

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Co-authored-by: ionitron <hi@ionicframework.com>
Co-authored-by: Giuliana Silva <108938618+OS-giulianasilva@users.noreply.github.com>

packages/vue/src/proxies.ts

@@ -379,6 +379,7 @@ export const IonGrid = /*@__PURE__*/ defineContainer<JSX.IonGrid>('ion-grid', de
 
 export const IonHeader = /*@__PURE__*/ defineContainer<JSX.IonHeader>('ion-header', defineIonHeader, [
   'collapse',
+  'divider',
   'translucent'
 ]);