Contribute to the welcome view/walkthrough

[isidorn]

Hi VS Code PM here 👋

As we have discussed in the VS Code - Typescript sync it would be great if Typescript could contribute to the welcome view.
A great example of a language that has already done this are Java and Python. I think Typescript should follow in those footsteps.

Code pointer for python example https://github.com/microsoft/vscode-python/blob/main/package.json#L103
Docs https://code.visualstudio.com/api/references/contribution-points#contributes.walkthroughs

fyi @DanielRosenwasser