chore: Update tsconfig target to ES2019

[just-boris]

Issue #, if available:

Description of changes:

Follow up for #163. We could not make es2021 syntax work, because some of our consumers do not support optional chaining syntax in their build tools, but we can do es2019 syntax + es2021 lib

Dry-run to live: 7572150327

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.78%. Comparing base (193e04b) to head (4a2cfb1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #169   +/-   ##
=======================================
  Coverage   98.78%   98.78%           
=======================================
  Files          36       36           
  Lines         904      904           
  Branches      243      255   +12     
=======================================
  Hits          893      893           
  Misses         11       11           

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