Introduce DotNetBuildOuterRepo control

[mmitche]

See https://microsoft-my.sharepoint.com/:w:/p/mmitche/EdchH8A4okpOoKhkki1sJEYB0LyAaaCyX5_6A887gL744Q?e=JERvht for full design:

When “true”, indicates that the infrastructure is executing within outer repo build or inner repo build phases
This is essentially ArcadeBuildFromSource or ArcadeBuildVertical.

Should be active when in the outer build or inner build (when invoked from the outer build)

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[mmitche]

Arcade changes complete.

[mmitche]

Changes now complete in orchestrator.