Support storing cephfs omap in a different namespace in rados under same filesystem metadata pool

[Madhu-1]

Describe the feature you'd like to have

Support storing cephfs omap in a different namespace in rados under the same filesystem metadata pool

What is the value to the end user? (why is it a priority?)

With this feature, even the metadata of the pvc/subvolumes will be stored under a different namespace, where security/isolation is the priority the user/customers can configure csi to use a different namespace.

How will we know we have a good solution? (acceptance criteria)

We can have a new field in the configmap where we have an entry for the subvolumegroup name.

[zerotens]

Hello together, funny story.
I wrote today a PR, but i didn't see the issue and that @iPraveenParihar was already working on it.
https://github.com/ceph/ceph-csi/compare/devel...zerotens:cephfs-namespace?expand=1

Is this reasonable to you or do you really want to make it configurable via configmap which would need many function calls as the constant is used in many places.