Add Sangfor AD exporter

[shaxiaozz]

https://groups.google.com/g/prometheus-developers/c/jHROaPs0g0U

[jan--f]

Hello from the bug scrub!
Thank you for your contribution. I'm afraid we need to decline this for now. We are happy to feature exporters that are actively developed and used. Unfortunately this one has so far only a limited community behind it and seemingly low adoption. Please try again at a later stage.
The exporter itself could use a few improvements with regards to the Prometheus data model (e.g. don't export rates but rather counters and let Prometheus calculate rates, see https://prometheus.io/docs/instrumenting/writing_exporters/).

[shaxiaozz]

@jan--f okk,thank you.