chore: Revert "chore: upgrade lambda and codebuild default runtime from nodejs16.x to nodejs18.x"

[iamhopaul123]

Reverts #5429 because we can't use SDK v2 in our custom resource code. Adopting to SDK v3 takes more effort. Reverting the PR for now to unblock the other PRs.

[github-actions]

🍕 Here are the new binary sizes!

Name	New size (kiB)	size (kiB)	Delta (%)
macOS (amd)	52208	51976	+0.45
macOS (arm)	53064	52812	+0.48
linux (amd)	45924	45716	+0.45
linux (arm)	45252	45060	+0.43
windows (amd)	43368	43168	+0.46

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.91%. Comparing base (cce61ba) to head (64a57b6).
⚠️ Report is 207 commits behind head on mainline.

Additional details and impacted files

@@             Coverage Diff              @@
##           mainline    #5432      +/-   ##
============================================
- Coverage     69.91%   69.91%   -0.01%     
============================================
  Files           299      299              
  Lines         45484    45484              
  Branches        295      295              
============================================
- Hits          31801    31799       -2     
- Misses        12137    12140       +3     
+ Partials       1546     1545       -1     

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