C# extension should use .NET Install Tool to find SDK

[claudiaregio]

[Kiryonn]

Is it really a good idea ? In my humble opinion, it would make more sense for .NET Install Tool to be an optional dependency instead of a required one. When we already have one or more SDKs, experienced user might just want to point to it, without having an extension that pings a server every time they connect to their IDE. Not to mention an extension that enables telemetry by default. This change would make the .NET Install Tool even more of a dependency than it should.