Rename test example to gateway example

[leducp]

Meaningless example folder name, renamed to a real meaningful name.

[github-actions]

File	Coverage	Lines	Branches
All files	39%	58%	21%	❌
lib/include/kickcat/Error.h	79%	75%	83%	✅
lib/include/kickcat/Mailbox.h	86%	87%	85%	✅
lib/include/kickcat/protocol.h	88%	88%	0%	✅
lib/include/kickcat/CoE/EsiParser.h	0%	0%	0%	❌
lib/include/kickcat/CoE/OD.h	0%	0%	0%	❌
lib/master/include/kickcat/Bus.h	60%	100%	20%	❌
lib/master/include/kickcat/DebugHelpers.h	83%	100%	66%	✅
lib/master/include/kickcat/Gateway.h	75%	100%	50%	✅
lib/slave/include/kickcat/AbstractESC.h	0%	0%	0%	❌
lib/slave/include/kickcat/ESC/EmulatedESC.h	0%	0%	0%	❌
simulation/network_simulator.cc	0%	0%	0%	❌

Minimum allowed coverage is 75%

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