* Make `async:true` the default for `invoke` calls (#3750)
* Switch away from native grpc impl. (#3728)
* Remove usage of the 'deasync' library from @pulumi/pulumi. (#3752)
* Only retry as long as we get unavailable back. Anything else continues. (#3769)
* Handle all errors for now. (#3781)
* Do not assume --yes was present when using pulumi in non-interactive mode (#3793)
* Upgrade all paths for sdk and pkg to v2
* Backport C# invoke classes and other recent gen changes (#4288)
Adjust C# generation
* Replace IDeployment with a sealed class (#4318)
Replace IDeployment with a sealed class
* .NET: default to args subtype rather than Args.Empty (#4320)
* Adding system namespace for Dotnet code gen
This is required for using Obsolute attributes for deprecations
```
Iam/InstanceProfile.cs(142,10): error CS0246: The type or namespace name 'ObsoleteAttribute' could not be found (are you missing a using directive or an assembly reference?) [/Users/stack72/code/go/src/github.com/pulumi/pulumi-aws/sdk/dotnet/Pulumi.Aws.csproj]
Iam/InstanceProfile.cs(142,10): error CS0246: The type or namespace name 'Obsolete' could not be found (are you missing a using directive or an assembly reference?) [/Users/stack72/code/go/src/github.com/pulumi/pulumi-aws/sdk/dotnet/Pulumi.Aws.csproj]
```
* Fix the nullability of config type properties in C# codegen (#4379)
Fix the following warning and turn on "treat warnings as errors" for our .NET projects.
```
Deployment/InvokeOptions.cs(6,60): warning CS1574: XML comment has cref attribute 'InvokeAsync{T}(string,
```
After creating an initial Pulumi .NET project, it will be natural for some folks (who are unfamiliar with Pulumi) to try to run it via `dotnet run`, as that's how you'd typically run a .NET Core program. Doing so today fails with:
```
Unhandled exception. System.InvalidOperationException: Environment did not contain: PULUMI_MONITOR
at Pulumi.Deployment..ctor()
at Pulumi.Deployment.RunAsync(Func`1 func)
at Pulumi.Deployment.RunAsync(Func`1 func)
at Pulumi.Deployment.RunAsync(Action action)
at Program.Main() in /Users/user/temp/quickstart/Program.cs:line 9
at Program.<Main>()
```
Instead, provide a more descriptive error message indicating that the pulumi CLI should be used to run the program. We return the same error as we do for Node.js and Python.
```
Unhandled exception. System.InvalidOperationException: Program run without the Pulumi engine available; re-run using the `pulumi` CLI
at Pulumi.Deployment..ctor()
at Pulumi.Deployment.RunAsync(Func`1 func)
at Pulumi.Deployment.RunAsync(Func`1 func)
at Pulumi.Deployment.RunAsync(Action action)
at Program.Main() in /Users/user/temp/quickstart/Program.cs:line 9
at Program.<Main>()
```
