[Merged by Bors] - Implement unprivileged mode

[nightkr]

Description

This adds support for running as an unprivileged container (mostly fixes #243).

Sadly, it doesn't run rootless per se, since we need those privileges to register the CSI plugins, but it at least lets containerd/k8s keep some of its sandboxing.

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

Beta Give feedback

1. Changes are OpenShift compatible
2. CRD changes approved
3. Helm chart can be installed and deployed operator works
4. Integration tests passed (for non trivial changes)

Reviewer

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1. Code contains useful comments
2. (Integration-)Test cases added
3. Documentation added or updated
4. Changelog updated
5. Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

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1. Feature Tracker has been updated
2. Proper release label has been added

Once the review is done, comment bors r+ (or bors merge) to merge. Further information

[nightkr]

It has been ok'd by @lfrancke, so ready for review.

[sbernauer]

Tested using helm install secret-operator stackable-test/secret-operator --version 0.0.0-pr252 --set securityContext.privileged=false

[nightkr]

bors r+

[bors]

Pull request successfully merged into main.

Build succeeded:

• All tests passed