Add Symbols Authentication Support for TraceEvent

[brianrob]

• Creates a new symbols authentication NuGet package to be used alongside TraceEvent. This ensures that non-Microsoft internal users are not subjected to all the new authentication-related dependencies.
• Moves symweb authentication into the new NuGet package. Additional auth mechanisms can be moved to be available to TraceEvent, but this is beyond the scope of this PR.
• Creates a samples application to show users how to setup authentication when using SymbolReader.