Add cable ID field to connections

[XioNoX]

Currently the power, console, and interfaces connections are defined the following way:
device_a,interface_a,device_b,interface_b,connection_status

It would be useful (at least to us) to be able to define a cable ID as we label all our connections/cables (including power and console).
It could also be in the form of a generic "notes/label" field, or allowing custom fields for connections.

[XioNoX]

@jeremystretch I looked for duplicates before opening that task, but couldn't find any. Could you point me to the one I should follow instead?
Thanks

[DanSheps]

Probably because it is related to #20

[jeremystretch]

Searching the issues for "cable ID" shows duplicate issues #2271, #1291, and #589, all of which reference #20.