Introduce Kind for artifact data

[mmitche]

This is a replacement for PublishFlatContainer, with the intention of extending this to include PDBArtifacts, so that we can remove the separate handling of these prior to build promotion. Kind has 2 current types, and is valid on artifact data: Package and Blob. If Kind is set, it overrides the PublishFlatContainer setting for the given artifact. Otherwise the existing defaults/behavior are used.

To double check:

• The right tests are in and the right validation has happened. Guidance: https://github.com/dotnet/arcade/blob/main/Documentation/Validation.md

[mmitche]

@ViktorHofer Needs local verification.

[ViktorHofer]

I think you also want ItemsToPushToBlobFeed items that are manually added by repos to respect that new metadata. The best place to do that would be here:

arcade/src/Microsoft.DotNet.Arcade.Sdk/tools/Publish.proj

Lines 238 to 245 in bbea86c

	<ItemGroup>
	<ItemsToPushToBlobFeed>
	<!-- Default artifact visibility is External -->
	<Visibility Condition="'%(ItemsToPushToBlobFeed.Visibility)' == ''">$([MSBuild]::ValueOrDefault('$(DefaultArtifactVisibility)', 'External'))</Visibility>
	<!-- Default to IsShipping=true -->
	<IsShipping Condition="'%(ItemsToPushToBlobFeed.IsShipping)' == ''">true</IsShipping>
	</ItemsToPushToBlobFeed>
	</ItemGroup>