metrics-exporter-prometheus: Add API to initialize HTTP listener from existing TcpListener

[michelhe]

This commit adds a new API to the PrometheusBuilder that allows users to provide their own configured TCP listener. The use case is to enable users to configure the TCP listener before passing it to the exporter - for example, to set socket options or bind to port 0 and retrieve the port number assigned by the OS.

My own use case for this is to use port=0 and then grab the port, log it and then give it to PrometheusBuilder

[tobz]

I do intend to look at this soon, but changes to PrometheusBuilder that add additional variants are usually low down on my list: it already contains a large number of methods, which makes trying to thinking through if we really should add something take a little more time.

[tobz]

The more I looked at it, the more I thought it's probably OK to add another method for now. 🤷🏻

Left one comment about cleaning up the doc comment for the new method.

[michelhe]

The more I looked at it, the more I thought it's probably OK to add another method for now. 🤷🏻

Left one comment about cleaning up the doc comment for the new method.

Great, thanks for the consideration and willingness to upstream it! :)
I'm just not too fond of the method name I chose if this gets upstreamed. For my own fork I didn't care much 😛