Update default configuration for ssl to 'allow'

[alexandre-normand]

What does this PR do?

This updates the default config for ssl from disable to allow. The reason is that postgres 15 on RDS is switching the default for force_ssl to true. Setting the default to allow means that a failure to connect without ssl will trigger an attempt to connect using ssl.

We could also consider going a bit further and setting the default to prefer which means ssl would be used first but I went with a more conservative approach that's closer to our current value (prefer non-ssl and switch to ssl on failure).

Motivation

Help make for a smoother transition for RDS Postgres users when they upgrade to postgres 15.

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Changelog entries must be created for modifications to shipped code
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.

[codecov]

Codecov Report

Merging #15917 (a88af0a) into master (b3ba56f) will increase coverage by 0.11%.
Report is 6 commits behind head on master.
The diff coverage is 100.00%.

Flag	Coverage Δ
activemq	?
cassandra	?
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
postgres	91.84% <100.00%> (-0.07%)	⬇️
presto	?
solr	?
tomcat	?
weblogic	?

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[github-actions]

Test Results

     12 files       12 suites   16m 57s ⏱️
   236 tests    234 ✔️   2 💤 0 ❌
1 422 runs  1 374 ✔️ 48 💤 0 ❌

Results for commit a88af0a.