Add new color Labels

[simurai]

This adds a few new colored Labels to match the color roles in Primitives.

Before

After

This is part of https://github.com/github/primer/issues/331. On dotcom we still have a few deprecated Labels. Once this PR is published, we can replace them like:

Before	After
Label--info	Label--accent
Label--warning	Label--attention
Label--orange	Label--severe
Label--purple	Label--done
Label--pink	Label--sponsors

[changeset-bot]

🦋 Changeset detected

Latest commit: 6d9fd00

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/css	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[jonrohan]

Been waiting on that Label--sponsors so we can remove Label--pink