Allow copyright statement in footer to be set via Nunjucks macro

[frankieroberto]

Currently the copyright statement in the footer component is hardcoded, which means it can’t be set by the Nunjucks macro. The guidance on the page suggests that the copyright can vary:

The NHS website is (c) Crown copyright but the NHS generally does not have Crown status. The service manual footer, for example, says (c) NHS England.

To allow for both options, we add an additional option to the Nunjucks macro, with NHS England remaining as the default option.

This would follow the approach of the GOV.UK Design System footer component.