Consider caching dmsg entries

[jdknives]

Originally by @nkryuchkov

It might possible to store all existing dmsg entries in dmsg client and synchronize them with dmsg discovery every N seconds. The advantage is a decreased load of dmsg discovery. The disadvantage is a possible inconsistency of entries within N seconds.

[0pcom]

This is still a valid potential improvement. But moreso than just entries, we should probably have a way to update the dmsg servers in the dmsghttp-config or else store that in a temporary file and refer to that file on subsequent connections / invocations. Mainly for if something breaks or if the embedded list of dmsg servers change their ip addresses.