Registry ATA uses should be configurable

[sandersn]

Currently typingsInstaller always uses the NPM registry to install types-registry and @types/* packages. #33791 makes it use the github package registry for types-registry, with a fallback to NPM. But this is hard-coded. Instead the editor should pass a flag to typingsInstaller that specifies the registry to use.

It is fine if NPM is still the fallback -- in fact it is desirable until we're confident in github's ability to host packages.

[sandersn]

After discussing this, we decided that this feature doesn't make sense with Microsoft owning both github and npm. There's no gain in redundancy anymore.