FsToolkit.ErrorHandling 2.0.0-beta001

- Switches TaskResult Library from TaskBuilder to Ply. Credits [Nino FLoris](https://github.com/NinoFloris) - (https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/97) - This change replaces [TaskBuilder](https://github.com/rspeele/TaskBuilder.fs) with [Ply](https://github.com/crowded/ply). Ply has better performance characteristics and more in line with how C# handles Task execution. To convert from TaskBuilder to Ply, replace the namespace of `FSharp.Control.Tasks.V2.ContextInsensitive` with `FSharp.Control.Tasks.NonAffine`. - This also removes the TargetFramework net461 as a build target. Current netstandard2.0 supports net472 fully according to [this chart](https://docs.microsoft.com/en-us/dotnet/standard/net-standard#net-implementation-support). It's recommended to upgrade your application to net472 if possible. If not, older versions of this library, such as 1.4.3, aren't going anywhere and can still be consumed from older TargetFrameworks.