Merge logger categories and document them

[jander-msft]

From #424:

@jander-msft I expected to be able to remove metrics logging with:
Logging__LogLevel__Microsoft.Diagnostics.Monitoring.RestServer.Controllers.MetricsController

but I'm still seeing logging from Microsoft.Diagnostics.Monitoring.RestServer.OutputStreamResult. We should consider using the parent controller category for OutputStreamResult.

We should probably look at merge several of the categories together, simplifying their names, and documenting them.