ci: add snapshot release workflow

[pfulton]

Inspired by @GarthDB and Spectrum Tokens, this adds an on-demand snapshot release workflow.

Any user with write access can trigger the workflow to run against a branch and a snapshot release will be published from that branch based upon the changeset(s) added to the branch's commit history.

For example:

1. I make some changes to the project, and push up my changes to a branch.
2. I add a changeset to signify that my changes should incur some version increase.
3. I navigate to the Actions tab in the GitHub interface, and click on Release Snapshot from the list of available workflows in the left navigation.
4. Once there, I click on Run Workflow in the upper right part of the interface, which shows a popover.
5. In the popover, I choose the branch from which I wish to release the snapshot ("Use workflow from"), and in the text field, I type in a meaningful tag name (example: s2-action-button)—or, optionally, I leave this field blank and the workflow attempts to automatically create a tag name based on the branch's name.
6. The workflow runs, using changeset version to version the affected components with the proper snapshot version name and tags, and it also automatically publishes to npm with the snapshot version number and tags.

Description

How and where has this been tested?

Please tag yourself on the tests you've marked complete to confirm the tests have been run by someone other than the author.

Validation steps

Regression testing

Validate:

1. The documentation pages for at least two other components are still loading, including:

• The pages render correctly, are accessible, and are responsive.

7. If components have been modified, VRTs have been run on this branch:

• VRTs have been run and looked at.
• Any VRT changes have been accepted (by reviewer and/or PR author), or there are no changes.

Screenshots

To-do list

• I have read the contribution guidelines.
• I have updated relevant storybook stories and templates.
• I have tested these changes in Windows High Contrast mode.
• If my change impacts other components, I have tested to make sure they don't break.
• If my change impacts documentation, I have updated the documentation accordingly.
• ✨ This pull request is ready to merge. ✨

[changeset-bot]

⚠️ No Changeset found

Latest commit: 143ca23

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]

🚀 Deployed on https://pr-3071--spectrum-css.netlify.app

[github-actions]

File metrics

Summary

Total size: 4.10 MB^*

🎉 No changes detected in any packages

* Size determined by adding together the size of the main file for all packages in the library.
* Results are not gzipped or minified.
* An ASCII character in UTF-8 is 8 bits or 1 byte.

[castastrophe]

I love this! Thanks for adding it. Would you add the instructions you wrote up for the description to the release instructions in the Storybook guides? 🎉