Removes PnP Transformation projects and related documentation and files. Closes #1742

[Adam-it]

🎯 Aim

The aim is to remove the transformation projects from the PnP.Core package, as it was kind of an experimental feature, we agreed not to continue, mainly due to the fact there are other products and native integrations in Microsoft 365 that allow migration from SP OnPrem and other vendors to SharePoint Online

✅ ToDo

• Project clean up
• Documentation clean up
• Mark PnP.Core.Transformation and PnP.Core.Transformation.SharePoint as deprecated in nuget.org

🔗 Related

Closes #1742

[Adam-it]

⚠️ BEFORE WE MERGE

we should definetly mark the PnP.Core.Transformation and PnP.Core.Transformation.SharePoint NuGets as deprecated in nuget.org.

@jansenbe most probably I will need your help with that

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.25%. Comparing base (63545f3) to head (f50f78f).
⚠️ Report is 2904 commits behind head on dev.
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Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1755      +/-   ##
==========================================
- Coverage   82.42%   81.25%   -1.17%     
==========================================
  Files         416      637     +221     
  Lines       28590    45388   +16798     
  Branches        0     4778    +4778     
==========================================
+ Hits        23565    36880   +13315     
- Misses       5025     7099    +2074     
- Partials        0     1409    +1409     

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