Backup implementation: controller, plugins, collection, webhooks

[zerospiel]

Backup implementation main part contains the following changes:

• install velero via flux rather than code
• adjust roles for the velero chart
• remove unnecessary controller values
• rename Backup to ManagementBackup
• remove Oneshot parameter from the Spec
• add StorageLocation to both Management and ManagementBackup
• remove unused types
• manage schedules in the ctrl instead of velero
• new source runner for schedules
• collect the required velero backup spec for the whole backup
• label Credential references (clusterIdentities) in order to include them in backup
• backup validation webhook
• amend backup controller logic with better objects handling
• fix bug in providertemplates ctrl when ownerreferences are being updated but requeue is not set
• add custom plugins set via mgmt spec
• rename k0smotron related provider labels to the correct ones from the k0sproject

To properly test the feature:

• have k0rdent instance (better with a clusterdeployment ready) with this PR
• install backupstoragelocation for velero, e.g.

---
apiVersion: v1
data:
  # base64 decoded AK/SK, e.g. 3 lines:
  # [default]
  # aws_access_key_id = <key>
  # aws_secret_access_key = <secret_key>
  cloud: <base64>
kind: Secret
metadata:
  name: cloud-credentials
  namespace: kcm-system
type: Opaque
---
apiVersion: velero.io/v1
kind: BackupStorageLocation
metadata:
  name: default
  namespace: kcm-system
spec:
  config:
    region: <eu-central-1> # region with an s3 bucket
  default: true
  objectStorage:
    bucket: <bucket-name> # bucket name
  provider: aws
  credential:
    name: cloud-credentials
    key: cloud

• enable backup in the management, set .spec.backup to the something like {enabled: true; schedule: "@every 5m"}
• wait for the scheduled backup to be created
• fully drop the k0rdent instance (imitate a disaster)

The restoration process:

• install clean k0rdent installation (without mgmt/releases/etc)
• install backup location (see above) to be able to fetch backups from a cloud storage
• perform velero restore (e.g. velero restore create <name> --existing-resource-policy update --from-backup <backup-name>)
• wait for the restore in the Completed state (e.g. with velero restore get)
• done

#814

[eromanova]

LGTM in general but the backup logic requires final approval from Andrey.

[zerospiel]

Should chart versions be updated because of the change to the provider label values?