WSL.Container API for existing containers and sessions

@craigloewen-msft is already working on this.

Since Jul 7, 2026.

**Is your feature request related to a problem? Please describe.**
While testing the new SDK the program crashed.
Next time it failed to create the container because one with that name already existed.
Right now it does not appear that there is a way to manage already existing containers.

**Describe the solution you'd like**

```C#
public class Session
{
public static void TerminateSession(string name);
public IReadOnlyList GetContainers();
public Container? OpenContainer(string name); //Open existing container
}

class SessionSettings
{
public bool OpenExisting { get; set; }
public bool ReplaceExisting { get; set; }
}

class ContainerSettings
{
public bool ReplaceIfExist { get; set; }
}
```

**Describe alternatives you've considered**

```bash
wslc.exe --session MySession system session terminate
wslc.exe --session MySession container list --format json --all
wslc.exe --session MySession stop MyContainerName
wslc.exe --session MySession rm MyContainerName
```

**Additional context**
Add any other context or screenshots about the feature request here.

NuGet: Microsoft.WSL.Containers 2.9.3
wslc 2.9.3.0