Change default user id and gid

[lfrancke]

Description

Part of stackabletech/issues#645

Change default user id and gid to the same ones we use in the operators themselves.
These are only the defaults that are used when a Pod does not specify their own securityContext.runAsUser or runAsGroup.

As of now all our operators do set these (and fsGroup) to 1000 and 0 respectively.
As the next step we want to remove that hardcoding so the default would then fall back to what we specify here.

Therefore I do believe that this PR should be a simple change with no downstream consequences.

Definition of Done Checklist

• Changes are OpenShift compatible
• Add an entry to the CHANGELOG.md file
• Integration tests ran successfully

TIP: Running integration tests with a new product image

The image can be built and uploaded to the kind cluster with the following commands:

bake --product <product> --image-version <stackable-image-version>
kind load docker-image <image-tagged-with-the-major-version> --name=<name-of-your-test-cluster>

See the output of bake to retrieve the image tag for <image-tagged-with-the-major-version>.

[stackable-bot]

All committers have signed the CLA.