Lambda Deploy: use Lambda dotnet tooling instead of SAM CLI?

AWS Toolkit for VSCode depends on [sam](https://github.com/aws/aws-sam-cli) to build/run/deploy Lambda projects (including .NET Lambdas). And sam doesn't appear to understand aws-lambda-tools-defaults.json.

For .NET Lambdas we might want to consider leveraging https://github.com/aws/aws-dotnet-deploy instead of SAM CLI, if (1) it is found on the system and (2) the project appears to be compatible with that tooling (instead of SAM CLI).

For reference: the older/legacy .NET lambda tooling took the form of `dotnet lambda`,

- source code here: https://github.com/aws/aws-extensions-for-dotnet-cli
- it supported a bespoke config file called `aws-lambda-tools-defaults.json`

Alternatively, we are considering support for "deploy configurations" in https://github.com/aws/aws-toolkit-vscode/issues/1052

Start by tracing the current SAM CLI build, run, and deploy path for .NET Lambda projects. Compare its project detection and configuration handling with aws-dotnet-deploy, including whether the tool is installed, and review the linked deploy-configurations issue 1052. Done would require a decided integration approach and clear compatibility criteria.

Written by the indexing model from the issue text.