Allow Crown copyright notice to be removed

[paulrobertlloyd]

Split off from #3873 and closes #1290

This PR may be a bit contentious, and relates to using govuk-frontend outside the realms of central government (i.e. usage by local authorities or at-length/corporate entities) and in community projects (i.e. X-GOVUK) where Crown copyright isn’t applicable.

There are few limitations with the footer regarding this currently. While you can change the copyright text, the following features remain hard coded:

• The copyright notice links to this page on The National Archives
• The copyright notice is always shown with the royal coat of arms above it

I considered providing a set of options to allow each of these aspects to be undone, perhaps by introducing a separate crownCopyright option that is overruled if a copyright option is provided… but this started to feel a bit too heavy handed and added needless complexity.

So instead I’m suggesting allowing for the Crown copyright statement to be removable. If a user wants to added their own copyright, they could include this using the contentLicence option. (A separate PR is needed to opt-out of showing the OGL logo.)

This is how the footer looks without the Crown copyright notice:

Related issue: #1290

[paulrobertlloyd]

Alternatively, remove the Royal Coat of Arms from the footer entirely. See #4019 (comment)

[colinrotherham]

@paulrobertlloyd I've rebased this PR for you and linked it with #1290

We made a few Nunjucks description tweaks recently so you'll see another commit + CHANGELOG entry

Will see if the team can give it a 2nd review

[querkmachine]

Hi @paulrobertlloyd,

This has spawned a few internal conversations about white-labelling elements of Frontend like the header and footer. I think that, should we wish to do so, we'd rather do that as a single cohesive piece of work rather than letting things be added or removed piecemeal.

Our guidance for now is if a service needs a footer that is significantly different to the one included in Frontend, the service should create their own fork of the component. For the time being, I'm gonna close this off.