[T/BHE] Sandwich benchmark for algebraic BC feature

set T_BHE to secondary variable

[Test/BHE] add temperature Dirichlet boundary condition on the BHE side of the model

remove gml and use new mesh structure

Add Sandwich Benchmark for Algebraic BC feature

Add alg_BC prj for Beier Sandbox

Add algebraicBC beier sandbox benchmark in xml format

Add algebraicBC fixed_power_constant_flow benchmark in xml format

Add process tag linear, input file