Feature/add xlsx support

[barisgit]

• Allow using xlsx and xls to import parts
• Update example csv to better show what is possible
• Add required tests (PASS)
• Fix parts merger when using update from info supplier and consider parts that already have a spn populated

[codecov]

Codecov Report

❌ Patch coverage is 77.50000% with 36 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.08%. Comparing base (8b417d6) to head (bbe4b01).

Files with missing lines	Patch %	Lines
src/Services/EntityMergers/Mergers/PartMerger.php	5.00%	19 Missing ⚠️
src/Services/ImportExportSystem/EntityImporter.php	83.52%	14 Missing ⚠️
src/Services/ImportExportSystem/EntityExporter.php	94.23%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #981      +/-   ##
============================================
+ Coverage     59.83%   60.08%   +0.25%     
- Complexity     6050     6067      +17     
============================================
  Files           529      529              
  Lines         20625    20748     +123     
============================================
+ Hits          12341    12467     +126     
+ Misses         8284     8281       -3     

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