[Spike] Investigate how the operator could support the upgrade and downgrade of its operands

[rm3l]

Add issues to #33 depending on the investigation findings.

[nickboldt]

possible workflow:

• delete current subscription for an installed RHDH 1.2 (operator and operands should persist; pods will stay running)
• install a new subscription and set to manual upgrade, with a startingCSV version set to an older version (eg., 1.1)
• subscription should then roll our replacement pods from 1.1 instead of 1.2

something like this is needed:

apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: rhdh
  namespace: NAMESPACE_VALUE
spec:
  channel: fast
  installPlanApproval: Manual
  name: rhdh
  source: SOURCE_VALUE
  sourceNamespace: openshift-marketplace # or other catalog source
  startingCSV: STARTING_CSV_VALUE

[rm3l]

Will be tracked under the rollback epic: https://issues.redhat.com/browse/RHIDP-3151