MissingPage: support multiple action buttons

[marshmalien]

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.

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Jira Issue: PF-4547