A few notes on this PR:

This PR will report resources that have drifts and those that have configuration differences in separate status fields; it will also report the drift/diff details in the structured form of JSON patches to allow better readability.

There has been discussions regarding:

a) report diffs as a CRP condition, with the diff details being explained as a condition message; i.e., drifts will have per-resource details, diffs will only have a cluster-scoped summary.

This PR:

status:
  placementStatuses:
  - clusterName: bravelion
    driftedPlacements:
    - resourceIdentifier:
        kind: Deployment
        name: app
      observedDrifts: ...
    diffedPlacements:
    - resourceIdentifier:
        kind: ConfigMap
        name: app
      observedDiffs: ...
    ...
  ...

The condition form:

status:
  placementStatuses:
  - clusterName: bravelion
    driftedPlacements:
    - resourceIdentifier:
        kind: Deployment
        name: app
    conditions:
    - type: ResourceDiffed
      message: ConfigMap resources `work/app` and 3 more are observed to have configuration differences
    ...
  ...

b) instead of using structured drift/diff details in the JSON patch format, we produces a summary string of JSON patches as the drift diff details

Structured form (this PR):

observedDrifts:
  - op: replace
     field: /spec/replicas
     oldValue: 1
     value: 2
  - op: add
     field: /spec/revisionHistoryLimit
     value: 5
  ...

Summary form:

drifts have been found in the resource: if applied, in the live state "/spec/replicas" (value: "2", oldValue: "1") and 4 more path(s) will be replaced; "/spec/revisionHistoryLImit" (value: "5") and 1 more path(s) will be added.

The concern is mostly that we would like to strike a balance between simplicity (CRP status is already an overburdened struct) and usefulness/being informative (users can find out exactly where goes wrong).

It is true that K8s objects are not the best place to put drift/diff details; but we do not have an CLI/UI available yet.

Of course none of these are function blockers.