Retain checked state when using nunjucks macros

[kr8n3r]

by @gazjoy, moved from govuk-design-system-backlog

Hi folks, I am using GOV.UK Prototype Kit v7.0.0-beta.10 and have an issue with the kit when using the checkbox macro and data on a checked item, see demo code.

Expecting:

1. I check a check box and continue
2. I view check answers and click change
3. My previous answer is retained

Actual:

1. I check a check box and continue
2. I view check answers and click change
3. My previous answer is not retained

When I want to change one of the answers on this screen I revisit the page and the checked item is no longer checked. I can also trigger the issue by clicking back in the journey and refreshing the page. When I use the HTML instead to the nunjucks macro adding {{ checked("contact-preference", "contact-preference-text") }} I see the expected result.

[kr8n3r]

solved by using checked function. need to add guidance how to use data in nunjucks macros
will be addressed by #563