Prometheus Exporter HTTP Server Support

Is your feature request related to a problem?
Yes. Currently, Java and Python do not implement an HTTP server in their language’s Prometheus exporter while node.js and Go do implement a server. For the C++ implementation, we have a choice between implementing the HTTP server or not implementing it. Benefits of implementing the HTTP service include that it is user friendly and conforms to the Prometheus exporter structure (Java and Python split it up into two pieces). Cons of implementing the HTTP service include this implementation could be the extra work that comes with creating it, managing it, and closing it.

Describe the solution you'd like
Implementing the HTTP server would make use of the C++ Prometheus exporter easier for end users. It also would make it easier for members in the future to contribute when working on related features.

Describe alternatives you've considered
Alternatively, not implementing the HTTP server would still be a feasible option. Java and Python both don’t implement an HTTP server in their exporter, instead opting to split up the implementation into two separate pieces.

No files, tests, or entry points are named. Start by reviewing the existing C++ Prometheus exporter and comparing the server approaches described for the node.js, Go, Java, and Python implementations. Done means the project has a decided HTTP-server approach with its lifecycle and user-facing behavior defined and implemented.