Add content from drafts to their final location

[romaricpascal]

What

Update the pieces of content drafted for this release with their final version:

• update the "Unreleased" section with the drafted release notes (internal)
• check link to updated logo SVG in the CHANGELOG points to its latest version from this PR
• update the browser-support.md with its final drafted content (internal)
• replace all links to the Frontend Docs preview (release-5-0--govuk-frontend-docs-preview.netlify.app) with links to the live site (frontend.design-system.service.gov.uk)
• replace all links to the Design System preview (release-5-0--govuk-design-system-preview.netlify.app) with links to the live site (design-system.service.gov.uk)

Why

To make sure that the content is up to date before the release

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• [x] CHANGELOG is up to date
• [x] Browser support docs are up to date
• [x] Links to preview sites point to live site

[romaricpascal]

To limit the time spent reviewing the release PR, I've put it as its own issue. If we prefer spending a little more time reviewing and doing that while we update the CHANGELOG as part of https://github.com/alphagov/govuk-frontend/issues/4515, that works as well.