Add "Read roboport contents" as a roboport circuit network mode of operation.

[NeuralParity]

The currently available mode of operations are: "Read logistic network contents", and "Read robot statistics". As far as I can tell it is not possible to determine how many/what type of robots and/or repair packs are in a roboport.

Proposal:
Add a third mode of operation "Read roboport contents".

This mode will return the contents of the roboport (in the same way connecting a chest does).