update the cephblockpool reonciler to disable mirroring

[rewantsoni]

When mirroring on storageCluster was disabled, the cephblockpool mirroring was not disabled, this could break the DR as MCO enables/disables the mirroring on the cephblockpool via storageCluster.

Hence, with this PR we are making the mirroring spec on the storageCluster as a pointer and enabling/disabling mirroring on cephblockpool only if the value is set. If mirroring is set to nil other controller will be able to make changes on the mirroring field on the cephblockpool.

[rewantsoni]

Testing:

[rewantsoni odf] k get storagecluster ocs-storagecluster -oyaml | yq '.spec.mirroring' && k get cephblockpool ocs-storagecluster-cephblockpool -oyaml | yq '.spec.mirroring'
null
{}

Enabled from storageCluster:
[rewantsoni odf] k get storagecluster ocs-storagecluster -oyaml | yq '.spec.mirroring' && echo "" && k get cephblockpool ocs-storagecluster-cephblockpool -oyaml | yq '.spec.mirroring'
enabled: true
peerSecretNames:
  - ux-cert-secret

enabled: true
mode: image
peers:
  secretNames:
    - ux-cert-secret

Disable from storageCluster:
[rewantsoni odf] k get storagecluster ocs-storagecluster -oyaml | yq '.spec.mirroring' && echo "" && k get cephblockpool ocs-storagecluster-cephblockpool -oyaml | yq '.spec.mirroring'
enabled: false

{}

Not set on storageCluster:
[rewantsoni odf] k get storagecluster ocs-storagecluster -oyaml | yq '.spec.mirroring' && echo "" && k get cephblockpool ocs-storagecluster-cephblockpool -oyaml | yq '.spec.mirroring'
null

enabled: true
mode: image

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: iamniting, rewantsoni

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[rewantsoni]

/cherry-pick release-4.17

[openshift-cherrypick-robot]

@rewantsoni: new pull request created: #2796

In response to [this](https://github.com/red-hat-storage/ocs-operator/pull/2795#issuecomment-2348862594): >/cherry-pick release-4.17 Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository.