Move chromatic into a reusable workflow

[sndrs]

What are you changing?

• pulls chromatic into a reusable workflow
• uses it:
  • following a successful run of validate in CI
    • after a push to main
    • on PRs with the run_chromatic label
    • on PR from dependabot or changesets release bot
  • when a run_chromatic label is added to a PR

Why?

this should maintain the same level of chromatic coverage, but detaches CI from the labelling trigger in PRs

[changeset-bot]

⚠️ No Changeset found

Latest commit: b86c0d5

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

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

[github-actions]

Tip

Once this PR is ready to go, add the run_chromatic label to run the Chromatic tests.

This saves us a lot of money by not running the tests before we need them.

[oliverabrahams]

Looks good!