Feature Request: Add Resource Settings to initContainers for vtbackup

Currently, the InitContainers section in the vtbackup pod spec does not expose the ability to define container resources.
This causes the deployment to fail in k8s clusters that enforce setting container resources.

13m         Warning   CreateFailed               vitessshard/vtcluster-test-unsharded-x-x-95cb1c8e                           failed to create Pod vtcluster-test-unsharded-x-x-vtbackup-init-1dbe7505: pods "vtcluster-test-unsharded-x-x-vtbackup-init-1dbe7505" is forbidden: failed quota: platform-dbtech-vt16-override-test-resources: must specify limits.memory for: init-vt-root; requests.cpu for: init-vt-root; requests.memory for: init-vt-root

We workaround this issue by defining a limitrange such as this

apiVersion: v1
kind: LimitRange
metadata:
  name: limitrange
spec:
  limits:
  - default:
      memory: 512Mi
    defaultRequest:
      cpu: "1"
      memory: 512Mi
    type: Container

Ask: Would be good to expose this ability so that we can get away from relying on the limitrange.

Start in pkg/operator/vttablet/vtbackup_pod.go, at the InitContainers section around lines 152-169, and trace how the vtbackup pod spec is built. Expose resource settings for the init container and verify that generated pods satisfy clusters requiring CPU and memory requests and limits.