fix(PostgresDatabaseAdapter): error handling for new participant

[nicky-ru]

• Added handling for unique constraint violation to log a warning if a participant already exists.
• Improved error logging to include userId and roomId for better traceability.

What kind of change is this?

• feat: (new feature)
• fix: (bug fix)
• chore: (updates to dependencies or build processes)
• docs: (documentation changes)
• style: (formatting, missing semi colons, etc; no code change)
• refactor: (refactoring production code)
• test: (adding tests, refactoring tests; no production code change)
• perf: (performance improvements)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.82%. Comparing base (7904298) to head (4e83a05).

❌ Your project status has failed because the head coverage (50.82%) is below the target coverage (70.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #113   +/-   ##
=======================================
  Coverage   50.82%   50.82%           
=======================================
  Files         180      180           
  Lines       24413    24413           
  Branches     2243     2243           
=======================================
  Hits        12407    12407           
  Misses      11962    11962           
  Partials       44       44           

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