[feature] Set the default root password for the cluster.

[runkecheng]

Is your feature request related to a problem? Please describe.

Now the default root password is empty. Percona will only set a root password at initialization, which will cause the root password of default deployment cluster to be empty, and cannot modify the root password through YAML, this is not safe.

	// +kubebuilder:default:=""
	// +kubebuilder:validation:Pattern="^$|^[A-Za-z0-9@#$%^&*_+\\-=]{8,32}$"
	RootPassword string `json:"rootPassword,omitempty"`

Describe the solution you'd like

• Set default value for the ROOT password

• Instructions for this situation in Sample Yaml

Describe alternatives you've considered

Additional context

[runkecheng]

https://github.com/percona/percona-docker/blob/main/percona-server-5.7/ps-entry.sh