docs: add details metrics and telemetry services setup

[cusma]

I was wondering if we needed any details on how the metrics and telemetry services are setup? They happen before the algod server initialization, but doesn't really have anything to do with the operation of the server itself.
There isn't much detail about them outside of the appendix, which are just configuration options, so would require a reader to look at the implementation directly if they were interested to learn about it.

Originally posted by @nullun in #181 (comment)