Implement "Footer" pattern

Implement a "Footer" pattern which can be shared / re-used by other web-applications:

Existing implementations:

• The existing salary scale 'app' contains the basic Drupal D7 footer,
• The ballots application contains the same footer implemented in Django,
• The Web Platform showcase site shows the new footer design,
• The Figma footer designs: https://www.figma.com/design/MFwGcqcZCTZkV8lrJL95lJ/CWP-components?node-id=566-3441&p=f&t=r59zZMn7Qv0SL2k9-0