Investigate and fix our Windows pipelines being slow to start

It takes 10 minutes to get to the point where Go is installed and ready to run the tests.

• 3-4 minutes of this is starting a Windows instance. We can get this down to 30-40 seconds by moving our Windows instance to fleeting in AWS, backed by a warm pool (stopped) instances.
• 6-7 minutes to download and install the Windows Go MSI.