`aspire update` command

[mitchdenny]

We want to implement an aspire update command on the CLI. The goal of this command is to update the SDK and package references in an app host project as well as package references in referenced projects.

It should probably build upon any prior art that we have in the .NET SDK, but it will likely need to go further to support polyglot scenarios if we end up having packages for other languages/frameworks.

We probably want to have it be an interactive experience where the developer can run it locally and confirm each update as we suggest it (so they know what changed).

[mitchdenny]

/cc @davidfowl @maddymontaquila @melytc @DamianEdwards

[DamianEdwards]

I think dotnet add package is the existing CLI command to update a package (yes it adds or updates). So I imagine aspire update would need to first discover referenced Aspire packages via dotnet msbuild and some filtering to packages starting with known Aspire prefixes, before running dotnet add package for each one. I'm a bit concerned this might not be nice and fast as we won't be able to parallelize it. It might be better to actually do this manually so we can optimize it.

We'll also need to deal with the SDK reference which AFAIK has no CLI experience to manipulate, so if we have to deal with that manually it might be just as easy to do all of it ourselves.