Change our start page to the new Getting Started experience

[bwateratmsft]

Announced here: https://code.visualstudio.com/updates/v1_57#_new-getting-started-experience, https://code.visualstudio.com/updates/v1_56#_welcome-page-walkthroughs

Extensions can contribute walkthroughs.

[bwateratmsft]

Tagging this experimentation. The C++ extension team has a way to properly set up these walkthroughs as experiments, and this is obviously a screamingly good candidate for experimentation.

[bwateratmsft]

This may have to wait for VSCode 1.59, as it contains fixes that are necessary to make start pages experiment-able. I believe that 1.59 is releasing in the next few days. Depending on uptake it may or may not make sense to put this feature into 1.17.0.

[BigMorty]

Sounds good.

[bwateratmsft]

Steps we might like:

• Add Dockerfiles
• Edit Dockerfiles (lang server, intellisense, etc.)
• Build image
• Run containers
• Docker explorer
• Publish to cloud (e.g. Azure if Azure Account extension installed?)
• Further reading (docs, issues page, etc.)