Include a page template within the nhsuk-frontend npm package

[frankieroberto]

Currently the Service Manual documents a Page template, but a page template is not actually included within the nhs-frontend npm package itself.

There is a layout.njk file within the repository, but that is used only for the site used for previewing and testing the components, and isn’t part of the published package.

The Prototype kit also has a template.html (confusingly in the docs/ folder) which is similar (but not identical).

I think ideally we’d include a page template within NHS Frontend, and then use that from within the Prototype Kit. Any other downstream users of NHS Frontend which use Nunjucks could also then use that.