feat!: remove the helm test connection Pod

The chart shipped a `helm test` hook Pod that ran `wget` against the HTTP Service. It only proved that the
Service resolves and answers on the configured port, which the readiness probe already covers, so it carried
no information the release did not have anyway. In exchange it pulled `busybox:latest` into clusters -- an
unpinned, mutable tag in a chart that otherwise pins every image digest -- and it kept a Pod spec alive that
had to track every change to the security context and hostUsers helpers.

Removing the template also removes the `test.*` values that only existed to configure it, so the parameter
table in the README was regenerated accordingly.

A guard in `deprecation.yaml` catches leftover `test` values instead of silently ignoring them. Its message
deviates from the surrounding guards on purpose: there is no replacement value to point at, so it states that
the feature is gone rather than suggesting a migration target.

BREAKING CHANGE: `helm test <release>` no longer executes any test for this chart, and the values
`test.enabled`, `test.image.name` and `test.image.tag` have been removed. Installations that still set them
will fail with a descriptive error until the keys are dropped, unless `checkDeprecation` is set to false.

Co-authored-by: Copilot <copilot@github.com>

values.yaml

@@ -1299,15 +1299,7 @@ postgresql:
 # Set it to false to skip this basic validation check.
 ## @section Advanced
 ## @param checkDeprecation Set it to false to skip this basic validation check.
-## @param test.enabled Set it to false to disable test-connection Pod.
-## @param test.image.name Image name for the wget container used in the test-connection Pod.
-## @param test.image.tag Image tag for the wget container used in the test-connection Pod.
 checkDeprecation: true
-test:
-  enabled: true
-  image:
-    name: busybox
-    tag: latest
 
 ## @param extraDeploy Array of extra objects to deploy with the release.
 ##