Support the experimentation platform

[bobbrow]

We want this for our "getting started" work.

[sean-mcmanus]

What is the experimentation platform? Is it fixed by #7512 ?

[Colengms]

The module involved is vscode-tas-client. It would be a replacement for our A/B testing approach and use of cpptools.json.

It allows retrieval of variables from 'control tower', which can be varied based on the 'treatment' of the client (whether the client is selected for an experiment or not).

There is a TAS-Client repo in DevOps (in DivDev) that contains some documentation. (I don't want to link it here, since it's internal).

It was suspected that this might be required for the Getting Started walkthrough work, but experiments related to who that is enabled for are handed by VS Code and not the extension itself. Since it's relatively simple to use, I'd like to wait until we have an experiment to run (so we have a reason to actually call into it) before doing this work. Otherwise, referencing the module and initializing it would seem have no particular use.