Allow localisation of content licence and copyright notices in Footer

[querkmachine]

This are the bare minimum changes needed for enable localisation of the Footer component's content licence and copyright notices. In this case, it is assumed that an Open Government Licence (OGL) and Crown copyright are still being used, and that the notices are only being translated into another language.

This differs slightly from the internationalisation spike work, as I've split the contentLicence and copyright parameters into html and text versions to facilitate extending them with more options, as described below.

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Issues #1290 and #1291 originally asked that it be possible to remove the OGL and Crown graphics. This hasn't been done in this PR, as it isn't strictly needed for the current localisation work and (for the most part) public-facing GOV.UK services will have been made available under OGL and Crown copyright.

I've created a version of this work with more customisation options, including changing/removing the Crown copyright URL and removing the licence/copyright graphics, as a separate branch. You can compare those branches here. Whether we consider these changes necessary or not is up for discussion!

[vanitabarrett]

This PR makes sense to me (although needs tests and a Changelog entry to make it 'release ready' - aware it's still in draft). I'm happy to do just what's needed to enable internationalisation, although can see benefits of the other approach too. If we go with this PR, do you think it would then involve a breaking change to introduce the ability to completely override the logo etc too?

[querkmachine]

@vanitabarrett I don't think anything in this PR would block us expanding it to include the other options at a later date.

[querkmachine]

I've added a changelog entry but was a little unsure of how to focus it (as 'customisation', as 'localisation', as 'translation'), as it can now be changed, but still practically has to be OGL and Crown copyright.

Can you give an expert opinion, @claireashworth?

[claireashworth]

Having the focus as localisation seems sensible to me. If the focus is customisation we should refer to the information from the National Archives as they own/manage the licence and copyright.

[vanitabarrett]

All works well, just a few comments about expanding the documentation/examples

[vanitabarrett]

Looks good to me! Would be great to get the commits tidied up/squashed a bit before merging.

[vanitabarrett]

Looks good to me 🎉