WIP: DO NOT MERGE: Add protoconf submodule

A temporary submodule to allow testing the prototype of the new configuration framework. The core in the submodule repository will be distributed across the various projects once a bit more mature.

How to test the new configuration

1. Get a full project checkout setup, e.g. https://gitlab.cern.ch/lhcb/upgrade-hackathon-setup/
2. Clone the submodule (if not done already) and rebuild

cd Phys
git fetch
git checkout add-submodule
git submodule update --init
cd ..
make Phys

3. Try out some option files

Phys/run gaudirun.py Phys/Phys/PhysConf/python/PhysConf/protoconf/HLT1Opts.py
Phys/run gaudirun.py Phys/Phys/PhysConf/python/PhysConf/protoconf/HLT1OptsWithLines.py