Add magnet auto-configuration for HLT

Merged Frank Winklmeier requested to merge fwinkl/athena:hlt_magfield into master

Add back the code that is responsible for the magnet auto-configuration based on the currents in the configuration ptree when running online or in Add a "Modifier" to enable the auto-configuration by default in

In addition, make sure the file input peeking is only done in and not

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