Cut v0.4.0 release

[michelleN]

[kate-goldenring]

The plugin has been released. We can fully close this when the plugin has been merged into the spin-plugins repo: spinframework/spin-plugins#101

[michelleN]

Looks like it's been merged in spin-plugins so I'll mark this as done! Feel free to update if there are additional steps we need to wait for. Thank you!