Allow Pods to request only CA certificate

[nightkr]

There is a similar Issue for customers: #410

See https://stackable-workspace.slack.com/archives/C033A863YPL/p1697611851226539

[nightkr]

We should also have a user-facing API for this.

[sbernauer]

We should also have a user-facing API for this.

@nightkr created #410, hope that fits your needs

[nightkr]

Covered by #410.