[DBM][Postgres] Adds logical database breakdown for connection metrics

[aldrickdev]

What does this PR do?

This will add 2 new connection metrics that have a logical database breakdown.

• postgresql.database_connections
• postgresql.percent_database_usage_connections

Example of both metrics below:

Motivation

Customer Request -> SDBM-2452

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

[datadog-prod-us1-5]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.34%. Comparing base (31eda08) to head (b7998b2).
⚠️ Report is 10 commits behind head on master.

Additional details and impacted files

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[chatgpt-codex-connector]

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[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/changelog.d/22999.added
postgres/datadog_checks/postgres/postgres.py
postgres/datadog_checks/postgres/util.py