Refactor uninstall commands

[TinaMor]

PR description

Refactor the uninstall commands to only remove program data (program data folder, config files, env variable, and RegKeys) when the -purge flag is passed.

Github issue

Uninstall-Containerd too destructive #40

Background information

Running the uninstall command currently deletes the program data as well. This is too destructive as the user would like to retain these folders/files (e.g. Containerd snapshot folder) even after installing another version (either an upgrade or an upgrade).

To resolve this, we add a -purge flag that when passed in the uninstall command, the program data will be removed, otherwise, it will be retained.

Testing information

Examples: To uninstall containerd

1. WhatIf

   > Uninstall-Containerd -WhatIf
   
   What if: Performing the operation "Containerd will be uninstalled from 'C:\Program Files\Containerd'' and containerd service     will be stopped and unregistered" on target "COMPUTERNAME".

2. Retain the program data

   Uninstall-Containerd

3. Purge program data

   Uninstall-Containerd -Purge

Checklist

As part of our commitment to engineering excellence, before submitting this PR, please make sure:

• You've tested this code in both Desktop & Server environments and AMD & ARM64 enviroments (functional testing).
• You've added unit tests for new code.
• You've added/updated documentation in the cmdlet docs, command-reference.md and the modules help files.
• You've reviewed the PR/code best practices defined in the CONTRIBUTING.md.

In addition, after this PR has been reviewed, please agree to:

• If changes have been made to your PR in the process of addressing comments, please make sure to test again the final version in both AMD and ARM64 environments.
• Validate your changes have not introduced any regressions.