Amend contributing documentation with a guide on how we write C# Cmdlets for PowerShell

[vexx32]

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Is Your Feature Request Related To A Problem? Please describe.

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Describe The Solution. Why is it needed?

We need to amend the contribution documentation in this repository to include some information about how we tend to author C# cmdlets, classes and design patterns to make use of and those to avoid as well.

Specifically, we should include the following information:

• Cmdlets should inherit from ChocolateyCmdlet and not Cmdlet or PSCmdlet
• When and how to make use of SupportsShouldProcess aka -WhatIf / -Confirm
• Cmdlets should contain minimal to no core logic, anything that other cmdlets need to make use of should be provided as part of a helper class, since calling into other C# cmdlets is not something that can or should really be done directly.
• Usage and extension of existing helpers like PSHelper or ChocolateyCmdlet and so forth
• How to manage error handling, and where
  • Exceptions should be thrown in core logic, caught and rethrown using ThrowTerminatingError() or WriteError() in the cmdlet layer itself
• Dependency injection must be avoided, at least in anything that's in the cmdlet layer itself (inheriting ChocolateyCmdlet) as PowerShell does not support this.
• Some guidance on communication between Chocolatey CLI and cmdlets, which is typically mediated with environment variables.
• Under no circumstances should there be a direct dependency on CLI code from the cmdlets project, they need to remain separate.

Additional Context

No response

Related Issues

• Convert PowerShell Functions to C# CmdLets #3477