Run an internal pre-release to npm

[romaricpascal]

What

Run an undocumented, private pre-release, publishing an early version on our package on npm (proposing under an @internal tag).

Why

Validate that our pre-release process before actually publicly pre-releasing, as well as offer an easier way to integrate with the Prototype Kit's test to validate that things work OK.

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• Agree upon a name for the prerelease tag (internal?)
• Make the pre-release
• Update the Design System release branch (release/5.0) to use the pre-release and create any issue necessary if fixes are needed
• Update the Frontend docs release branch (release/5.0) to use the pre-release and create any issue necessary if fixes are needed

[colinrotherham]

Both preview PRs are now updated with the pre-release:

• Updates for GOV.UK Frontend v5.0.0 govuk-frontend-docs#333
• Updates for GOV.UK Frontend v5.0.0 govuk-design-system#2977

Moving this into "Needs review" for:

• Add pre-release documentation with version numbers #3977

[colinrotherham]

Having said that, our first internal pre-release is done

I'll split out PR #3977 separately on the board and close this