Introduce automated releases to CICD

[six7]

With the work done around fixing figcd we can now introduce Automated releases into our CI. We already checked if this works locally, and released a version of Apply variables through it.

Let's introduce this to the Figma plugin CI, to be done once the Version packages PR is merged.

• Make it so it uses the figma.version from the package.json instead of the package version
• Publish release to GitHub using the contents of the Version packages PR
• Publish a changelog to Featurebase using their API using the contents of the Version packages PR (without the extra content from Changeset)
• Perform the automated Figma release linking to the Featurebase changeset as Version info
• Post to Slack in the #releases channel using the contents of Featurebase and a link to the Featurebase changelog