Add default shell support to sshdconfig

[tgauth]

PR Summary

• update sshdconfig resource to include get & set to configure Windows registry for Win32-OpenSSH's default shell options

PR Context

• https://github.com/PowerShell/Win32-OpenSSH/wiki/DefaultShell

[Copilot]

Pull Request Overview

Adds support for configuring a default shell in the sshdconfig tool by wiring up new get/set commands to Windows registry keys, updating the DSC resource manifest, and providing Pester tests to verify behavior.

• Implement get/set for DefaultShell in Rust (src/get.rs, src/set.rs) with Windows registry integration
• Extend CLI with clap (src/args.rs, src/main.rs), update export behavior, and add JSON schema
• Add Pester tests (sshdconfig/tests/defaultshell.tests.ps1) and update DSC manifest (sshdconfig/sshd.dsc.resource.json) and packaging (build.ps1)

Reviewed Changes

Copilot reviewed 11 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
sshdconfig/tests/defaultshell.tests.ps1	New Pester tests for DefaultShell get/set on Windows and errors on non-Windows
sshdconfig/sshd.dsc.resource.json	DSC resource manifest exposing get/set commands for default shell
sshdconfig/src/set.rs	Windows registry write/remove logic for DefaultShell
sshdconfig/src/get.rs	Windows registry read logic for DefaultShell
sshdconfig/src/main.rs	Switch to clap for CLI parsing, wire up get/set/schema
sshdconfig/src/metadata.rs	Added RepeatableKeyword enum for future keywords
sshdconfig/src/error.rs	Added InvalidInput and RegistryError variants to error enum
sshdconfig/src/args.rs	Defined DefaultShell struct and Set subcommand schema
sshdconfig/src/export.rs	Changed export to print JSON directly
sshdconfig/Cargo.toml	Added clap and conditional registry_lib dependencies
build.ps1	Updated packaging entries for new resource manifest files

Comments suppressed due to low confidence (1)

build.ps1:64

• Packaging script references 'sshd_config.dsc.resource.json' but this file is not present in the repo. Ensure the file is committed or remove this entry from the build manifest.

    'sshd_config.dsc.resource.json',