Add support for disabling macro2md coupling per face

[Thinkpiet]

The current indexing system initialization code assumes that the MD domain is embedded in the CFD domain, i.e. that we want to couple macro-to-md on each of the 6 faces of the Mamico domain. TODO: allow disabling of coupling per face.

Suggested XML format in <mamico> config to configure this:
<enable-macro-to-md west="yes" east="no" north="no" south="no" bottom="no" top="no" />

Steps:

• Allow mamico config to read enable-macro-to-md tag
• Make the entire enable-macro-to-md tag optional
• Default option is west="yes" east="yes" north="yes" south="yes" bottom="yes" top="yes"
• Pass boundary infos to a new initialization method for IndexingService
• Configure the IndexTrait::md2macro domain via CellIndex::lowerBoundary and CellIndex::upperBoundary so that it includes the outerRegion at the faces where enable-macro-to-md is "no"
• Add unit test for new IndexingService initialization method, I guess this should simply be based on a few hardcoded examples