Kinetic diagonal stencil support

[SMijin]

The diagonal stencil can now take in another key - "harmonicOffset". This allows for harmonic coupling through that stencil.

For example a harmonic offset of -1 is equivalent to having f_{l-1} on the RHS. This should correctly perform interpolation for staggered harmonics.

Should be merged after #25

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 36 lines in your changes missing coverage. Please review.

Please upload report for BASE (dev-v1.3.0@052c506). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ic_models/kinetic_stencil_templates_procedures.f90	0.00%	31 Missing ⚠️
...nded_support/initialization_support_procedures.f90	0.00%	3 Missing ⚠️
...r_abstractions/composite_integrator_procedures.f90	0.00%	1 Missing ⚠️
..._secondary_el_source_term_generator_procedures.f90	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-v1.3.0      #26   +/-   ##
=============================================
  Coverage              ?   54.19%           
=============================================
  Files                 ?      239           
  Lines                 ?    10126           
  Branches              ?        0           
=============================================
  Hits                  ?     5487           
  Misses                ?     4639           
  Partials              ?        0           

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