fix: remove postgres example (security)

[pichlermarc]

The @opentelemetry/instrumentation-postgres example is outdated (OTel setup gets a tracer from the setup file instead of directly via the API) and (more importantly) the example server shows a questionable approach in building the SQL statement based on unsanitized user input. It's not exploitable as it's just an example (hence the Public PR) but I think it's still important to keep this out of examples 🙂

Happy to approve PRs re-adding an updated example in the future.

Edit: This also resolves a CodeQL alert and warnings that may be picked up by other automated code-scanning tools.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.09%. Comparing base (dfb2dff) to head (4571574).
Report is 101 commits behind head on main.

❗ Current head 4571574 differs from pull request most recent head 79f6122. Consider uploading reports for the commit 79f6122 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2171      +/-   ##
==========================================
- Coverage   90.97%   90.09%   -0.89%     
==========================================
  Files         146      140       -6     
  Lines        7492     6974     -518     
  Branches     1502     1473      -29     
==========================================
- Hits         6816     6283     -533     
- Misses        676      691      +15     

see 48 files with indirect coverage changes