Add dotnet package update command

[zivkan]

NuGet Product(s) Involved

dotnet.exe

The Elevator Pitch

Developers want to be able to easily update packages, without needing to edit project files.

It might not be well known, or intuitive, that dotnet package add can update packages, as well as add them. But there's many opportunities to improve the experience, such as updating multiple packages in one command, updating multiple projects in one command, even updating only packages with known vulnerabilities.

Additional Context and Details

Initial spec: #13961