metricbeat/module/postgresql: Improve healthcheck for Postgres

[shmsr]

What does this PR do?

Improve healthcheck for Postgres to reduce the flakiness in integration tests.

Why is it important?

Flaky tests lead to instability of CI and could lead to unnecessary blocking of PRs and unreliable tests. In my opinion, start_period and reason mentioned in peter-evans/docker-compose-healthcheck#16 (comment) is something that could help us as this improves healthcheck.

Also bumped the fallback version for the image to the latest minor of the same major release to avoid any issues. Currently, my latest major is 15 and currently, I've set the fallback version to 13.11 so that it doesn't change the major.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.
• I have made my commit title and message explanatory about the purpose and the reason of the change

How to test this PR locally

As the flaky tests are not reproducible, we'll do a soak testing i.e., soak it for some time to see if it really reduced the flakiness of integration tests or not.

Related issues

• Relates https://github.com/elastic/obs-infraobs-team/issues/1150
• Closes Build&Test / metricbeat-goIntegTest / TestFetch – github.com/elastic/beats/v7/metricbeat/module/postgresql/statement #35995 (comment)
• Relates https://github.com/elastic/obs-infraobs-team/issues/1150#issuecomment-1657968550
• Relates FATAL: role "root" does not exist peter-evans/docker-compose-healthcheck#16 (comment)
• Relates How to determine when new container is truly "ready" docker-library/postgres#146 (comment)
• Relates Use CMD instead of CMD-SHELL for --healthcheck-cmd moby/moby#28679

[botelastic]

This pull request doesn't have a Team:<team> label.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @shmsr? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[shmsr]

Keeping this PR in draft for some time to do some testing myself. But it is ready for review.

[elasticmachine]

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Build stats

• Start Time: 2023-08-01T06:00:23.298+0000

• Duration: 11 min 35 sec

❕ Flaky test report

No test was executed to be analysed.

🤖 GitHub comments

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To re-run your PR in the CI, just comment with:

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[shmsr]

/test metricbeat

[shmsr]

^^ Will retrigger a few times in order to test if Postgres tests are failing or not.

[shmsr]

/test metricbeat

[shmsr]

/test metricbeat

[shmsr]

/test postgres

[shmsr]

/test

[shmsr]

/test

[shmsr]

/test metricbeat-goIntegTest

[agithomas]

LGTM!