Library theming: Update the Background image component in design kit

[patternfly-jira-sync]

Update the Background image component in the PatternFly design kit to align with the unified theme. Update Figma files, styles, documentation, and ensure unified visual consistency throughout.

Deliverables:

• Include new variants

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Jira Issue: PF-4069

[patternfly-jira-sync]

Closed via Jira sync - Jira issue PF-4069 was closed.