Event source configuration

[twenzel]

Hi @hananiel,
I think this approach is a better event source configuration making it more flexible and more "explorable" for the developer.

[twenzel]

The configuration looks like

using var meterprovider = Sdk.CreateMeterProviderBuilder()
                    .AddEventCounters(options =>
                    {
                        options.AddRuntime().WithAll(); // all from 'System.Runtime'
                        options.AddAspNetCore() // dedicated event counters with optional mapped metric name
                            .WithCurrentRequests("http_requests_in_progress")
                            .WithFailedRequests()
                            .WithRequestRate()
                            .WithTotalRequests("http_requests_received_total");
                        
                        options.AddEventSource("Microsoft-AspNetCore-Server-Kestrel") // add any other event counter
                            .WithCounters("total-connections", "connections-per-second")
                            .With("connections-per-second", "The number of connections per update interval to the web server", MetricType.LongSum);
                    })

[hananiel]

this approach is great and user friendly but the eventCounters under well known counters are not the only ones. We also need to support ones we do not know about. So it has use types that allow users to add theirs without code changes. Also needs to be configurable from appsettings.json or other IConfiguration sources.