Change naming rule of Cronjob in order to extend name length limitation of MySQLCluster

[YZ775]

What

In the current version, the name length of MySQLCluster is limited to 40 characters because the name length of CronJob/StatefulSet is limited to 52 characters by Kubernetes.

40 characters are short in some cases. For example, large clusters and multi-tenant Kubernetes cluster. So we want to extend the length.

How

Ideas

• Change names of CronJob to moco-backup-<some random name> from moco-backup-<Cluster name>
• Shorten the prefix moco-backup

Limitation

• Even if the limitation of CronJob is solved by the effort above, there are still limitations by StatefulSet.
• The prefix of StatefulSet moco- is enough short. so it's hard to extend the limitation of MySQLCluster name to over 47 characters.

Checklist

• [ ] Finish implementation of the issue
• [ ] Test all functions
• [ ] Have enough logs to trace activities
• [ ] Notify developers of necessary actions

[YZ775]

We decided that we don't start implementation of this issue for now because it's merit is smaller than it's cost.