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 (182660b).
⚠️ Report is 36 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?

Review from nenadnoveljic is dismissed. Related teams and files:

• database-monitoring-agent
  • postgres/datadog_checks/postgres/data/conf.yaml.example

[github-actions]

⚠️ The qa/skip-qa label has been added with shippable changes

The following files, which will be shipped with the agent, were modified in this PR and
the qa/skip-qa label has been added.

You can ignore this if you are sure the changes in this PR do not require QA. Otherwise, consider removing the label.

List of modified files that will be shipped with the agent

postgres/datadog_checks/postgres/data/conf.yaml.example

[pierreln-dd]

I had an out-of date ddev version, decided it was easier to start fresh on a new PR: #21934