Feature: client config w/ multi-server support

[konradybcio]

Rough sketch:

~/.config/cdba/config

server1
   blah

server2
    blah

User runs:

cdba -l

User gets:

server1
 boardA-n
 boardB-m

server2
 boardA-k
 boardC-l

Additional ideas:

• Let the user request "boardA", grab the first available one (across servers and -numbers)
• Add preferred order / check ping/throughput for best ux
• Let the user specify "server1/boardA" and "server1/boardA-n" in case a specific board is of interest

[konradybcio]

Perhaps an "aggregator server" concept could be considered as well, as a single front-end e.g. for teams where the boards are distributed across multiple cdba servers instead, only requiring one config/keystore to be updated

[vinodkoul]

or have .cdba-config which has the server config, I would not prefer a central (thus fail prone) aggregator server