Describe the bug

Many commands that interact with NuGet have an --interactive flag that is used to signal that the user can be prompted for additional credentials. We should default this to 'true' instead of false so that user-driven sessions Just Work ™️.

We have several different --interactive flags that we should change at the same time, and we should have detection of common ways to signal that the session is not interactive:

• if stdin/stdout/stderr are redirected
• if we are not running in an interactive shell (in Unix this is commonly if the prompt environment variable PS1 is set)
• ???