Refactor uninstall to add -purge flag

[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 a downgrade).

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
   
   Confirm
   Are you sure you want to perform this action?
   Performing the operation "Containerd will be uninstalled from 'C:\Program Files\Containerd\bin' and containerd service will be stopped and unregistered.
   Containerd program data won't be removed. To remove program data, run 'Uninstall-Containerd' command without -Purge flag." on target "COMPUTERNAME".
   [Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"): Y
   
   Are you sure you want to uninstall Containerd?
   C:\Program Files\Containerd\bin
   [Y] Yes  [N] No  [S] Suspend  [?] Help (default is "Y"): Y
   WARNING: Uninstalling preinstalled Containerd at the path 'C:\Program Files\Containerd\bin'.
   Containerd will be uninstalled from 'C:\Program Files\Containerd\bin' and containerd service will be stopped and     unregistered. Containerd program data won't be removed. To remove program data, run 'Uninstall-Containerd' command without -Purge flag.
   Successfully uninstalled Containerd. 

3. Purge program data

   > Uninstall-Containerd -Purge
   
   Confirm
   Are you sure you want to perform this action?
   Performing the operation "Containerd will be uninstalled from 'C:\Program Files\Containerd' and containerd service will be stopped and unregistered. Containerd
   program data will also be removed." on target "COMPUTERNAME".
   [Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"): Y
   
   Are you sure you want to uninstall Containerd?
   C:\Program Files\Containerd
   [Y] Yes  [N] No  [S] Suspend  [?] Help (default is "Y"): Y
   WARNING: Uninstalling preinstalled Containerd at the path 'C:\Program Files\Containerd'.
   Containerd will be uninstalled from 'C:\Program Files\Containerd' and containerd service will be stopped and unregistered. Containerd program data will also be removed.
   Purging Containerd program data
   WARNING: Removing Containerd registry key
   WARNING: Removing Containerd program data
   WARNING: Removing Containerd from env path
   Removing containerd in User Environment Path
   Removing containerd in System Environment Path
   Successfully uninstalled Containerd.

TODOs not included in this PR

1. Unit tests for new functionality
2. Updating documentation for the -purge flag

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.

[iankingori]

Looks good