Additional data logging over CAN

Mark reports that we can only log channels that exist in the ecu already when using a second ecu to log data.

In this instance an MRE slaved to a proteus.

In order to record a steering angle with the MRE and log it in proteus it would have to be sent as "aux temp 2" for example and renamed after log is taken off the proteus.

We should find some way to rectify this either by adding some common body and extra sensor vales to the main firmware or allowing some arbitrary can channels to be logged.

No file, test, or entry point is named. Start by tracing how CAN channels are selected and logged across the MRE and Proteus firmware, then determine whether the intended solution is common sensor values or arbitrary channels; done means a steering-angle channel can be logged without repurposing and renaming an existing value.

Written by the indexing model from the issue text.