[DBMON-6003] Add Postgres unit tests to track all config default value changes

[eric-weaver]

What does this PR do?

The goal of this PR is to ensure our default config values remain the same. We're now explicitly asserting against all default rendered config values from InstanceConfig. Any changes to our hardcoded expected defaults will trigger a test failure with a clear message as to why it's failing and steps to take to mitigate. Similarly if new config values are added and they aren't asserted against in this test it will trigger a failure and require fixing up.

Example failure message when a new testConfig value is added but wasn't updated in the test

Motivation

The goal of this change is to ensure our config default values don't change unexpectedly or accidentally overtime to avoid regressions.

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

[github-actions]

⚠️ Recommendation: Add qa/skip-qa label

This PR does not modify any files shipped with the agent.

To help streamline the release process, please consider adding the qa/skip-qa label if these changes do not require QA testing.

[codecov]

Codecov Report

❌ Patch coverage is 50.63291% with 39 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.33%. Comparing base (8bc9b1d) to head (7940e26).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

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