K8SPS-348: add scheduled backups

[pooknull]

https://perconadev.atlassian.net/browse/K8SPS-348

DESCRIPTION

This PR adds a scheduled backup feature. A new section .spec.backup.schedule is added to the cr.yaml:

    schedule:
      - name: "sat-night-backup"
        schedule: "0 0 * * 6"
        keep: 3
        storageName: s3-us-west
      - name: "daily-backup"
        schedule: "0 0 * * *"
        keep: 5
        storageName: s3

CHECKLIST

Jira

• Is the Jira ticket created and referenced properly?
• Does the Jira ticket have the proper statuses for documentation (Needs Doc) and QA (Needs QA)?
• Does the Jira ticket link to the proper milestone (Fix Version field)?

Tests

• Is an E2E test/test case added for the new feature/change?
• Are unit tests added where appropriate?

Config/Logging/Testability

• Are all needed new/changed options added to default YAML files?
• Did we add proper logging messages for operator actions?
• Did we ensure compatibility with the previous version or cluster upgrade process?
• Does the change support oldest and newest supported PS version?
• Does the change support oldest and newest supported Kubernetes version?

[inelpandzic]

This looks good.

[JNKPercona]

Test name	Status
version-service	passed
async-ignore-annotations	passed
auto-config	passed
config	passed
config-router	passed
demand-backup	failure
gr-demand-backup	passed
gr-demand-backup-haproxy	passed
gr-finalizer	passed
gr-haproxy	passed
gr-ignore-annotations	passed
gr-init-deploy	passed
gr-one-pod	passed
gr-recreate	passed
gr-scaling	passed
gr-scheduled-backup	passed
gr-security-context	passed
gr-self-healing	passed
gr-tls-cert-manager	passed
gr-users	passed
haproxy	passed
init-deploy	passed
limits	passed
monitoring	passed
one-pod	passed
operator-self-healing	passed
recreate	passed
scaling	passed
scheduled-backup	passed
service-per-pod	passed
sidecars	passed
smart-update	passed
tls-cert-manager	passed
users	passed
We run 34 out of 34

commit: 9bfa4a1
image: perconalab/percona-server-mysql-operator:PR-716-9bfa4a12