GuestPortCurrentTel possible refactoring  #300

I've been thinking about the GuestPortCurrent message and I think it would be a lot nicer to do:

Proposed

// GuestPort current readings.
message GuestPortCurrent {
  message Currents {
    double vbat = 1;
    double v25 = 2;
    double v5 = 3;
  }

  Currents gp1 = 1;
  Currents gp2 = 2;
  Currents gp3 = 3;
  ...

Current

message GuestPortCurrent {
    ...
    double gp1_24v = 8; // Current on GP1 24V supply (A).
    double gp2_24v = 9; // Current on GP2 24V supply (A).
    double gp3_24v = 10; // Current on GP3 24V supply (A).
    double gp4_24v = 11; // Current on GP4 24V supply (A).
    double gp5_24v = 12; // Current on GP5 24V supply (A).
    double gp6_24v = 13; // Current on GP6 24V supply (A).
    double gp1_5v = 14; // Current on GP1 5V supply (A).
    double gp2_5v = 15; // Current on GP2 5V supply (A).
    double gp3_5v = 16; // Current on GP3 5V supply (A).
    double gp4_5v = 17; // Current on GP4 5V supply (A).
    double gp5_5v = 18; // Current on GP5 5V supply (A).
    double gp6_5v = 19; // Current on GP6 5V supply (A).
    ...

We could do this with a new message and keep the old one in parallel for a while (marked deprecated) with only the 3 old GPs it originally had.
A similar approach could be implemented for the error flags.

@follesoe @johannesschrimpf @sindrehan

Originally posted by @jp-pino in #272 (comment)