Add PackageProject installation for find_package support

[jonasbhjulstad]

Issue: It is not possible to: find_package(CXXGraph)
Changes:

1. Added CXXGraph Interface Library target
2. Added PackageProject Install configuration
3. Moved CXXGraphConfig.h to version.h for PackageProject compatibility

Usage:
find_package(CXXGraph)

target_link_libraries(<my_target> CXXGraph::CXXGraph)

[ZigRazor]

@jonasbhjulstad please correct build. Thank you.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.06%. Comparing base (8f05442) to head (14322af).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #553      +/-   ##
==========================================
+ Coverage   97.03%   97.06%   +0.03%     
==========================================
  Files          98       98              
  Lines       11356    11355       -1     
  Branches      799      799              
==========================================
+ Hits        11019    11022       +3     
+ Misses        337      333       -4     

Flag	Coverage Δ
unittests	97.06% <ø> (+0.03%)	⬆️

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