[AppInsights] Revisit dependency tracking category

[brettsam]

Dependencies are currently tracked with "Function.{FunctionName}", while user logs contain "Function.{FunctionName}.User". It seems like dependencies should have the "User" category as well.

The main scenario I see is that people want to remove the "Executed"/"Executing" traces that come with every invocation, yet keep their dependency tracking. But since they both are logged with "Function.{FunctionName}", there's no great way to do that today.