chore: add maryliag as CODEOWNER of opentelemetry-instrumentation-pg

[maryliag]

Add maryliag as CODEOWNER of plugins/node/opentelemetry-instrumentation-pg as discussed on SIG meeting of March 27.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.63%. Comparing base (dfb2dff) to head (77225d2).
Report is 510 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2052      +/-   ##
==========================================
- Coverage   90.97%   90.63%   -0.34%     
==========================================
  Files         146      146              
  Lines        7492     7488       -4     
  Branches     1502     1494       -8     
==========================================
- Hits         6816     6787      -29     
- Misses        676      701      +25     

see 8 files with indirect coverage changes

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[pichlermarc]

Thanks for picking up ownership of this component @maryliag 🙂