Stop secrets payload from ending in the MR and resolve it when used instead

[mad01]

Description of your changes

Change Observer loop not resolve secret in start of loop but rather resolve the secret in the create/update/delete funcs to not leak the secrets data in the the k8s MR object. Fixes #223

Description of your changes

I have:

• [x] Read and followed Crossplane's contribution process.
• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

manual test locally to see that the secret is not leaking in to the MR using this manifests. provider for testing have been started with --sanitize-secrets

---
apiVersion: kubernetes.crossplane.io/v1alpha2
kind: Object
metadata:
  name: secretpatch
spec:
  references:
  - patchesFrom:
      apiVersion: v1
      kind: Secret
      name: secretpatch
      namespace: crossplane-system
      fieldPath: data.sensitive
    toFieldPath: data.key-from-secret
  forProvider:
    manifest:
      apiVersion: v1
      kind: Secret
      metadata:
        namespace: default
      data: {}
  providerConfigRef:
    name: kubernetes-provider
---
apiVersion: v1
kind: Secret
metadata:
  name: secretpatch
  namespace: crossplane-system
type: Opaque
data:
  sensitive: cGFzc3dvcmQ=

[mad01]

I have looked at the test but could not see any clear way to add testing to confirm the new secrets logic