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

首先阅读 MissingPage 组件，并将其 footer API 与已经支持 customFooter 的 ErrorState 进行比较。确认现有的 toHomePageUrl action 是如何渲染的，然后添加一种受支持的方式来渲染多个自定义 action，同时保留当前行为。当使用方可以同时提供主页和返回 action，而无需复制 MissingPage 布局时，即表示完成。