Update query duration metrics in metadata.csv

[pierreln-dd]

What does this PR do?

Clarifies that postgresql.duration.* metrics (based on pg_stat_statement) are the values of completed queries

Motivation

Customer feedback

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.31%. Comparing base (95abfe3) to head (d455c36).
⚠️ Report is 25 commits behind head on master.

Additional details and impacted files

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Review from nenadnoveljic is dismissed. Related teams and files:

• database-monitoring-agent
  • postgres/metadata.csv

Review from nenadnoveljic is dismissed. Related teams and files:

• database-monitoring-agent
  • postgres/metadata.csv

[nenadnoveljic]

Is there a Jira card to link to this PR?