Update default configuration to collect postgres database by default

[alexandre-normand]

What does this PR do?

This PR aims to address confusion that comes up related to missing data due to the default postgres database being ignored. This updates the default configuration to enable data collection on the default database. We had talked about removing postgres from the default ignored_databases but since collect_default_database also directly relates to it, I think it makes sense to update both configuration defaults. For reference, here's where the collect_default_database gets used and how it relates to ignored_databases: https://github.com/DataDog/integrations-core/blob/master/postgres/datadog_checks/postgres/config.py#L73-L74.

Note that this is technically a breaking change because the collection behavior is going to change. We're going ahead with this change because it's going to be a better overall experience moving forward.

Motivation

Additional Notes

I validated the performance and impact of this on our integration environment. Note that I tested this change along with #12998 because they are both related to the same goal of reducing confusion regarding our data collection, going out at the same time. The material impact is that prior to both changes, query samples/activity was not collected on the default postgres database. With the two changes, they now are. And because query metric collection didn't honor the ignore_databases configuration before, query metrics on the default postgres database remains unchanged with the new default configuration.

Here's a clearer way to see the impact. This shows the different behavior of 7.39.0 vs the version with the changes with one deployment using the default config and another one setting collect_default_database to false.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[github-actions]

Label changelog/Changed was added to this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the changelog/Fixed label.

[github-actions]

Label changelog/Changed was added to this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the changelog/Fixed label.

[github-actions]

Label changelog/Changed was added to this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the changelog/Fixed label.

[github-actions]

The validations job has failed; please review the Files changed tab for possible suggestions to resolve.

[codecov]

Codecov Report

Merging #12999 (8ba5d45) into master (ed547c1) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Flag	Coverage Δ
postgres	91.87% <100.00%> (+0.19%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[jmeunier28]

lgtm