Add ability to add links into the footer

[cjrace]

There's a few examples of this starting to appear, e.g. on Explore education statistics we add a line about OSR and also links to various pages from the footer.

The UKHSA dashboard also does the same.

We can use the govuk-footer__inline-list class for this, and should make sure to give the option for a visually hidden heading that screen readers can use to navigate to these.

When we do this change, we should also add .noWS = "after" to the a tag for Open Government Licence as you can now remove the excess whitespace it adds pretty easily.

Example of current footer with whitespace is visible on the README

[cjrace]

Have an in progress version of this in https://github.com/dfe-analytical-services/apprenticeships-provider-dashboard