Add .NET instructions to workflows

A few of the workflows provide programming language specific instructions, i.e. the [code-simplifier](https://github.com/github/gh-aw/blob/main/.github/workflows/code-simplifier.md#phase-2-analyze-and-simplify-code). We should provide .NET instructions (based on the `dotnet` CLI) as well so that the workflows work out-of-the-box well with .NET.

Happy to submit a PR based on Copilot working on it.