Refactor: Adopt Flux runtime conditions and status standards

[stefanprodan]

Changes

• Make the Kustomization.status conform to the Kubernetes kstatus standard
• Make the Kustomization.status.conditions conform to the Kubernetes standard conditions
• Improve the reconciliation observability with real-time informations about the actions taken by the controller
• Adopt fluxcd/pkg/runtime/conditions and fluxcd/pkg/runtime/controller for status operations

Test image: ghcr.io/fluxcd/kustomize-controller:rc-747a2c9e

Reconciling status condition

This PR introduces a new status condition named Reconciling which improves the observability for the actions performed by the controller during a reconciliation run.

The Reconciling message reflects the current action being executed e.g.:

• Fetching manifests for revision X with a timeout of Y
• Building manifests for revision X with a timeout of Y
• Detecting drift for revision X with a timeout of Y
• Running health checks for revision X with a timeout of Y

The Reconciling condition is added to the status once the reconciliation starts and its Message is updated before each action performed by the controller during a reconciliation run.

conditions:
- lastTransitionTime: "2022-10-17T13:40:21Z"
  message: Running health checks for revision v1.0.0 with a timeout of 30s
  observedGeneration: 2
  reason: Progressing
  status: "True"
  type: Reconciling
- lastTransitionTime: "2022-10-17T13:40:21Z"
  message: Reconciliation in progress
  observedGeneration: 2
  reason: Progressing
  status: Unknown
  type: Ready

If the reconciliation encountered an error, the Ready condition is set to False and Reconciling is left in place, to signal that the controller will retry the failed action.

conditions:
- lastTransitionTime: "2022-10-14T17:50:57Z"
  message: Running health checks for revision v1.0.0 with a timeout of 30s
  observedGeneration: 2
  reason: ProgressingWithRetry
  status: "True"
  type: Reconciling
- lastTransitionTime: "2022-10-14T17:51:27Z"
  message: Timeout waiting for: [Job/default/test status: NotFound]
  observedGeneration: 2
  reason: HealthCheckFailed
  status: "False"
  type: Ready

If the reconciliation finishes with no errors, The Reconciling condition is removed from status and the Ready condition is set to True.

conditions:
- lastTransitionTime: "2022-10-14T17:51:27Z"
  message: 'Applied revision: v2.0.0'
  observedGeneration: 2
  reason: ReconciliationSucceeded
  status: "True"
  type: Ready

Closes: #663
Ref: fluxcd/pkg#380