* 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)
- Cache the username and last verified time associated with each logged-in
backend
- In the HTTP backend, verify the access token explicitly at most once
per hour
This trades off a little bit of usability for improved inner-loop
latency: if a user's API token becomes invalid less than an hour after
it was last verified, the user will see 4xx errors when attempting stack
operations rather than seeing the login prompt.
We move the implementations of our secrets managers in to
`pkg/secrets` (which is where the base64 one lives) and wire their use
up during deserialization.
It's a little unfortunate that for the passphrase based secrets
manager, we have to require `PULUMI_CONFIG_PASSPHRASE` when
constructing it from state, but we can make more progress with the
changes as they are now, and I think we can come up with some ways to
mitigate this problem a bit (at least make it only a problem for cases
where you are trying to take a stack reference to another stack that
is managed with local encryption).
