Add ability to override or remove Crown Copyright in Footer

[aliuk2012]

At the moment © Crown copyright in Footer is hardcoded text. User should be able to override this or remove it altogether.

Split from: https://github.com/alphagov/govuk-frontend/issues/971

Part of https://github.com/alphagov/govuk-design-system/issues/777

[aliuk2012]

Needed as part of https://github.com/alphagov/govuk-design-system-backlog/issues/185

[HughePaul]

This is needed for Welsh translations, which is required for a site to go into public beta.

[matthewmascord]

Hello, is there an ETA for this? Considering whether it's worth waiting or implementing our own fork of govukFooter.

[36degrees]

You can now override the 'crown copyright' text used alongside the crest in the footer (since v4.3.0), but you still can't remove it entirely.