Add "**" pattern trigger path handling

[dagood]

Right now Maestro supports an ending **/* explicitly, but not foo/**/bar or more complicated glob patterns. For orchestrated build final publish, we might want to trigger on dotnet/product/**/build.semaphore, for example.

Default approach is to add explicit ** support.

Another way is to let the subscription define a trigger regex rather than just glob matching. We can do both, eventually: better glob matching and regex support.