Default to installing the TLS CA into the operator's target namespace

[nightkr]

Description

See stackabletech/issues#498. OLM manifests are generated from the Helm charts, so fixing it in one should fix it in the other.

Note that this is a breaking change, existing users will need to either --set secretClasses.tls.caSecretNamespace=default or copy their CA secret across (kubectl -n default get secret/secret-provisioner-tls-ca -o json | jq '.metadata.namespace = "stackable-operators"' | kubectl create -f-).

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

# Author
- [ ] Changes are OpenShift compatible
- [ ] CRD changes approved
- [ ] CRD documentation for all fields, following the [style guide](https://docs.stackable.tech/home/nightly/contributor/docs-style-guide).
- [ ] Helm chart can be installed and deployed operator works
- [ ] Integration tests passed (for non trivial changes)
- [ ] Changes need to be "offline" compatible

# Reviewer
- [ ] Code contains useful comments
- [ ] Code contains useful logging statements
- [ ] (Integration-)Test cases added
- [ ] Documentation added or updated. Follows the [style guide](https://docs.stackable.tech/home/nightly/contributor/docs-style-guide).
- [ ] Changelog updated
- [ ] Cargo.toml only contains references to git tags (not specific commits or branches)

# Acceptance
- [ ] Feature Tracker has been updated
- [ ] Proper release label has been added
- [ ] [Roadmap](https://github.com/orgs/stackabletech/projects/25/views/1) has been updated

[razvan]

This prompted me to have a look at what we've done with 24.3 and it looks like default is hard coded there too.

Then I generated the manifests from this branch and saw that "default" is also used. This is understandable because there is no namespace set at the time when we generated the manifests.

So I think that this is a good fix for Helm but not for OLM where we probably need to interpolate the namespace from the environment at the installation time (or something like that).

I added a new task to this epic: stackabletech/issues#561

[nightkr]

This is still going to leave us in a better spot for OLM too though than we were in before, right? At least it would align with the default settings.

[razvan]

lgtm but maybe remove the Fixes reference to the issue before merging so that it's not closed automatically.