Trigger new link styles for government-frontend

[owenatgov]

What

Apply the feature flag for new link styles, from the latest release of GOV.UK Frontend, on this app.

Additionally updates the readme to include an example of a guide document and replaces instances of the .app-link class with .govuk-link--inverse.

Why

Part of an ongoing effort by the GOV.UK frontend community and GOV.UK Accessibility team to ensure that we are using the new design system link styles across our apps, ensuring that users reap the benefit of better link visibility.

Notes

• The government navigation menu at the top of some government frontend pages isn't using the new link styles properly. This is because this component is reliant on styles from the old "core" layout in static. I won't be pursuing getting these to work perfectly at the moment as the layout is due to be updated to the new "gem" layout in the immediate future, making any changes I make to this layout obsolete.
• I won't be including visual changes for all views as part of this PR as government-frontend pages all follow the same broad shape of breadcrumb, title, metadata, content. I will include one page to illustrate the link change.

List of links tested against by view

Link	Associated view
https://www.gov.uk/get-coronavirus-test	Answer
https://www.gov.uk/government/case-studies/how-the-dvla-deployed-a-chatbot-and-improved-customer-engagement	Case study
https://www.gov.uk/government/consultations/aligning-the-upper-age-for-nhs-prescription-charge-exemptions-with-the-state-pension-age	Consultation
https://www.gov.uk/government/organisations/hm-revenue-customs/contact/income-tax-enquiries-for-individuals-pensioners-and-employees	Contact
https://www.gov.uk/government/organisations/driver-and-vehicle-licensing-agency/about/complaints-procedure	Corporate info page
https://www.gov.uk/guidance/waste-exemption-nwfd-2-temporary-storage-at-the-place-of-production--2	Detailed guide
https://www.gov.uk/government/collections/eu-settlement-scheme-applicant-information	Detailed guide
https://www.gov.uk/government/fatalities/sergeant-simon-alexander-hamilton-jewell	Fatality notice
https://www.gov.uk/help/terms-conditions	Help page
https://www.gov.uk/government/publications/budget-2016-documents/budget-2016	HTML publication
https://www.gov.uk/log-in-register-hmrc-online-services	Guide
https://www.gov.uk/government/news/uk-travel-update-malta-added-to-green-list-and-green-watchlist-extended-as-plans-for-quarantine-free-travel-for-fully-vaccinated-passengers-from-ambe	News article
https://www.gov.uk/government/publications/the-national-minimum-wage-in-2021	Publication
https://www.gov.uk/business-finance-support/access-to-finance-advice-north-west-england	Specialist document
https://www.gov.uk/government/statistics/announcements/initial-findings-from-the-2021-census-in-england-and-wales	Statistics announcement
https://www.gov.uk/government/statistical-data-sets/unclaimed-estates-list	Statistical data set
https://www.gov.uk/government/speeches/19-july-remains-our-target-date-for-ending-restrictions	Speech
https://www.gov.uk/government/get-involved/take-part/volunteer	Take part
https://www.gov.uk/government/topical-events/2014-overseas-territories-joint-ministerial-council/about	Topical event about page
https://www.gov.uk/foreign-travel-advice/spain	Travel advice
https://www.gov.uk/government/groups/abstraction-reform	Working group
https://www.gov.uk/government/news/changes-to-secure-english-language-test-providers-for-uk-visas	World news story

Visual changes

Before	After

[alex-ju]

Looks good! We seem to have an .app-link class that could be replaced with .govuk-link--inverse, but not a blocker in switching to the new link styles, more of a 'nice to do' clean-up for us.

[owenatgov]

@alex-ju Good spot! I've updated instances of app-link with govuk-link--inverse as advised. I'm having some trouble with local testing at the moment so I'll look to test and merge this tomorrow.