Publish vscode extension to marketplace on release CI

[alt-romes]

Update the release CI (.github/release.yaml) to publish the built VSCode extension (.vix) to the marketplace (under https://marketplace.visualstudio.com/items?itemName=Well-Typed.haskell-debugger-extension)

[BinderDavid]

Consider also publishing to the open-vsx marketplace. It's actually super easy. We have a Github action that publishes to both marketplaces simultaneously here: https://github.com/polarity-lang/vscode/blob/main/.github/workflows/publish.yml

[alt-romes]

Open-vsx is tracked in #69