Add install scope to Windows installer options

[Xiaowen-Yang]

Add support for limiting Windows MSI install and uninstall options to a specific install scope.

The new system setting accepts:

• true for options that apply only to all-users installations;
• false for options that apply only to current-user installations; and
• "both" for options that apply to either scope.

When the setting is omitted, it defaults to "both" to preserve the existing behavior. Invalid values are rejected during configuration validation.

This change includes configuration validation, automated tests, Windows platform documentation, and a change note. The corresponding Windows app template change uses this setting to filter controls in the MSI install and uninstall dialogs.

Companion template branch:
beeware/briefcase-windows-app-template#113

Fixes #2986

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

Assisted-by: OpenAI Codex (GPT-5)

[freakboy3742]

Awesome! This works great in my testing - and the extra typos you've picked up in the docs are also helpful. Thanks for the PR!