ENH: Added pyproj.crs.CRS.to_3d

[snowman2]

• Related to Question: vertical transformation difference (PROJ 5.2 versus PROJ 8) OSGeo/PROJ#2609
• Tests added
• Fully documented, including history.rst for all changes and api/*.rst for new API

Would be good to have clarity on this before merging: OSGeo/PROJ#2614

[codecov]

Codecov Report

Merging #808 (ff60740) into master (d4f61f3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head ff60740 differs from pull request most recent head c36fbb1. Consider uploading reports for the commit c36fbb1 to get more accurate results

@@           Coverage Diff           @@
##           master     #808   +/-   ##
=======================================
  Coverage   95.13%   95.14%           
=======================================
  Files          21       21           
  Lines        1645     1647    +2     
=======================================
+ Hits         1565     1567    +2     
  Misses         80       80           

Impacted Files	Coverage Δ
pyproj/crs/crs.py	97.45% <100.00%> (+0.01%)	⬆️

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