Metrics published with wrong format

[rubur-webbeds]

With the latest release of Prometheus a new metrics' format is required in order to export them successfully.
Upgrading to the prometheus-net.AspNetCore v2.1.3 seems to be enough to publish metrics correctly.

[xordi]

In case you wold like to publish just ASP.NET Core metrics, I would recommend you to upgrade to prometheus-net 3.X and use the Metrics middleware included in this new version. In upcoming versions of Bluekiri.Diagnostics.Prometheus, the collection of metrics related to ASP.NET Core will be removed.

On the other hand, monitoring with the HttpHandlerDiagnosticListener, although still possible, will require some refactorings on the code to make it work properly with prometheus-net 3.0. There is an issue that must be resolved first by the prometheus-net team prometheus-net/prometheus-net#136. Currently we cannnot perform unit tests properly without this issue being fixed first.