Set up workflow to automatically publish release on new tags

[jodyheavener]

Right now when we want to put out a new version we need to:

1. Update the version in package.json, commit it
2. Create a new tag with the new version
3. Push to the remote
4. Publish the extension to the VS Code Marketplace locally (vsce publish)
5. Create a new VSIX file locally (vsce package)
6. Create a new Release with the VSIX file

Let's make this easier!

First, I realized Yarn has yarn version, so I've updated the README to document this and it'll take care of the first three steps.

Next I've added a new Workflow that takes care of the last three steps and does the following:

• Activates whenever a new tag beginning with a v is pushed.
• Sets the GITHUB_TOKEN permission such that it can write to the repo (this is used for the releases action)
• Sets up Node, Yarn, etc.
• Uses the HaaLeo/publish-vscode-extension GitHub Action to create a new release for the VS Code Marketplace.
  • Uses a VS_MARKETPLACE_TOKEN secret I've set up
  • Takes care of building and packaging everything
• Uses the softprops/action-gh-release GitHub Action to create a new GitHub Release in the repo
  • Defaults title of Release to tag name
  • The previous action provides us with a path to the VSIX file it just published so that we can attach it as a file to the Release