Improved shutdown and app configuration

[nagendramishr]

2.2.10.3

Proxy:

• OnShutdown: stop listening, begin aggressively event flushing => after timeout period: continue working, flushing events until done or killed.
• Begins to slow down connections when circuit breaker would trip
• Refactor app configuration code for readability and remove unnecessary code
• Server now slows down when number of memory events gets large
• Health probe now shows not-ready if number of unflushed events is large
• Update dotnet library versions

Nullserver:

• Updates to allow testing for streaming / non-streaming
• Allow tester to specify delay time

[ian-t-adams]

changes look clean and documentation is good