MultiClusterObservability stays in status "Installing"

Issue

• When creating a new MultiClusterObservability object, the installation progress stays on "Installing" and the following status is shown:

  $ oc get MultiClusterObservability -o yaml
  [..]
  status:
    conditions:
    - lastTransitionTime: "2021-08-13T07:49:42Z"
      message: Installation is in progress
      reason: Installing
      status: "True"
      type: Installing
    - lastTransitionTime: "2021-08-13T07:49:42Z"
      message: secrets "thanos-object-storage" not found
      reason: ObjectStorageSecretNotFound
      status: "False"
      type: Failed
  

• The MultiClusterObservability CRD shows an ObjectStorageSecretNotFounderror.