Add transform struct

[1-Bart-1]

Closes #209

• Adds a Transform struct, which is used in the SystemStructure to describe the orientation of the structure.
• Adds images to the documentation, which were removed when @example was removed.
• Improves the docs and docstrings

[codecov]

Codecov Report

Attention: Patch coverage is 89.58333% with 15 lines in your changes missing coverage. Please review.

Project coverage is 86.86%. Comparing base (d8b9f1b) to head (a12c598).
Report is 42 commits behind head on main.

Files with missing lines	Patch %	Lines
src/system_structure.jl	91.07%	10 Missing ⚠️
src/mtk_model.jl	63.63%	4 Missing ⚠️
src/symbolic_awe_model.jl	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #214      +/-   ##
==========================================
- Coverage   86.93%   86.86%   -0.08%     
==========================================
  Files           9        9              
  Lines        2005     2093      +88     
==========================================
+ Hits         1743     1818      +75     
- Misses        262      275      +13     

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