[release-1.21] Add events to deploy controller

[brandond]

Proposed changes

• Addresses issues with visibility (were errors encountered when parsing or applying the manifest) by adding change/failure events viewable via kubectl get events -n kube-system or kubectl describe addon -n kube-system <addon>. Events are inspired by k/k event behavior for Pods, where Events are created for container pull start, container pull success/failure, etc. They should be meaningful but not spammy.

Types of changes

• New feature

Verification

Note events when describing AddOn: kubectl describe addon -n kube-system coredns`

Linked Issues

• [release-1.21] Improve feedback of deploy controller operations and failures #3612

This is a stripped-down version of #2169 that only adds events; it doesn't attempt to address any of the other issues with tracking who modified the resource, since this can be (minimally) accomplished with #3433

Example output

Name:         traefik
Namespace:    kube-system
Labels:       <none>
Annotations:  <none>
API Version:  k3s.cattle.io/v1
Kind:         Addon
Metadata:
  Creation Timestamp:  2020-08-27T06:33:10Z
  Generation:          1
  Resource Version:  234
  Self Link:         /apis/k3s.cattle.io/v1/namespaces/kube-system/addons/traefik
  UID:               9485676f-0e38-481b-8989-b5efe3e43f1a
Spec:
  Checksum:  6d311bade7254b59e7b2bb3838032ab2686cb92d725408092f568960973927a6
  Source:    /var/lib/repos/k3s/server/manifests/traefik.yaml
Status:
Events:
  Type    Reason            Age   From                                Message
  ----    ------            ----  ----                                -------
  Normal  ApplyingManifest  30s   deploy, dev01.lan.khaus  Applying manifest at "/var/lib/repos/k3s/server/manifests/traefik.yaml"
  Normal  AppliedManifest   30s   deploy, dev01.lan.khaus  Applied manifest at "/var/lib/repos/k3s/server/manifests/traefik.yaml"

[galal-hussein]

LGTM