MissingPage: support multiple action buttons

Description

MissingPage currently supports only a single link/action via the toHomePageUrl prop (rendered as a "Go to home page" link). A common 404 page pattern includes multiple actions — typically both "Go Home" and "Go Back" buttons.

Use Case

In ansible/ansible-ui, our custom PageNotFound component renders two action buttons:

• "Go to Dashboard" (navigate to home)

• "Return to previous page" (browser back)

We cannot adopt MissingPage because it only renders one action.

Proposed Solution

Add support for custom footer actions, either via:

• A customFooter or actions prop that accepts ReactNode (most flexible)

• An additionalActions array prop alongside the existing toHomePageUrl

This would align with how other component-groups components like ErrorState support customFooter.

Current Workaround

We maintain a custom PageNotFound component that duplicates MissingPage's layout but adds a second button.

Jira Issue: PF-4547

まず MissingPage コンポーネントを読み、すでに customFooter をサポートしている ErrorState とその footer API を比較します。既存の toHomePageUrl アクションがどのようにレンダリングされるかを確認し、現在の動作を維持したまま複数のカスタムアクションをレンダリングできるサポートされた方法を追加します。MissingPage のレイアウトを複製せずに、利用側がホームアクションと戻るアクションの両方を指定できれば完了です。