CCM-9916: preload fonts with cross origin directive

[harrim91]

Description

• Self-host nhsuk fonts, which allows them to be loaded by Safari.
• Removes the upgrade-insecure-requests directive from CSP when running on localhost, which prevents Safari from trying to upgrade http localhost requests to https

Context

When opening notify.nhs.uk in Safari, the site failed to load fonts served from https://assets.nhs.uk.
The browser console showed:

Failed to load resource: Cancelled load to https://assets.nhs.uk/fonts/FrutigerLTW01-55Roman.woff2
because it violates the resource's Cross-Origin-Resource-Policy response header.

The site’s HTML was being served with:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

These headers enable cross-origin isolation. Under this policy, cross-origin assets must either:

• be fetched with CORS
• be served with a Cross-Origin-Resource-Policy (CORP) header of cross-origin or same-site.

Font fetches were happening from within a @font-face block in the nhsuk-frontend css. Safari was doing these fetches as no-CORS requests. The assets.nhs.uk server serves these fonts without a CORP header. So Safari was unable to load the fonts.

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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Sensitive Information Declaration

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.