Add ADMX definition for Group Policy

[florelis]

Adding definition file for a group policy. See #154

Still pending:

• Setting up localization for the strings.
• Figuring out a representation for the lists of allowed and additional sources. Currently it is only a list of name/value pairs but we can't represent all three of name, arg & type.

Code to respect the policy will come as a separate PR

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Misspellings found, please review:

• Aditional
• adml
• admx
• xsi

To accept these changes, run the following commands from this repository on this branch

pushd $(git rev-parse --show-toplevel)
perl -e '
my @expect_files=qw('".github/actions/spelling/expect.txt"');
@ARGV=@expect_files;
my @stale=qw('"validator valijson valueiterator "');
my $re=join "|", @stale;
my $suffix=".".time();
my $previous="";
sub maybe_unlink { unlink($_[0]) if $_[0]; }
while (<>) {
  if ($ARGV ne $old_argv) { maybe_unlink($previous); $previous="$ARGV$suffix"; rename($ARGV, $previous); open(ARGV_OUT, ">$ARGV"); select(ARGV_OUT); $old_argv = $ARGV; }
  next if /^(?:$re)(?:(?:\r|\n)*$| .*)/; print;
}; maybe_unlink($previous);'
perl -e '
my $new_expect_file=".github/actions/spelling/expect.txt";
use File::Path qw(make_path);
make_path ".github/actions/spelling";
open FILE, q{<}, $new_expect_file; chomp(my @words = <FILE>); close FILE;
my @add=qw('"Aditional adml admx xsi "');
my %items; @items{@words} = @words x (1); @items{@add} = @add x (1);
@words = sort {lc($a) cmp lc($b)} keys %items;
open FILE, q{>}, $new_expect_file; for my $word (@words) { print FILE "$word\n" if $word =~ /\w/; };
close FILE;'
popd

[JohnMcPMS]

I think @denelon needs to approve this for location and content.

We will need to investigate how to integrate this with the localization build; I can help inform you of how the current one works.

Not really part of the PR, but I think that we do need to have a process for how we release and version this as well. At a minimum, new policies will need documentation to indicate when they will be effective.

[florelis]

Using final names/strings from discussion with @denelon
Here's a summary:
File names: DesktopAppInstaller.adm[x,l]
Location of the policies in gpedit: Computer Configuration\AdministrativeTemplates\Windows Components\Desktop App Installer
Location of the backing registry keys: HKLM:\Software\Policies\Microsoft\Windows\AppInstaller
Policy names use "App Installer", descriptions use "Windows Package Manager"

I set the supported OS to SUPPORTED_Windows_10_0_RS3 = version 1709.

[denelon]

This looks good to me.