database root password pxc-root-password is not configurable

[ShuangMen]

Is your feature request related to a problem? Please describe.
This feature request is some sort related with the issue #1355

I deployed kubecf in my k8s cluster and for some reason I need to run 'helm uninstall' to remove the kubecf (Note here, I don't remove the pv of the database) and then 'helm install' kubecf again.
But this time the database fail to be running status and reports error message like "[Note] Access denied for user 'root'@'localhost' (using password: YES)"

This is because database still using the password of the previous deployment, but the new kubecf deployment generated a new value for pxc-root-password.

I see there is an option for external db to provide the root password

kubecf/chart/values.yaml

Line 389 in 92920b3

# root password (see `.variables.pxc-root-password`); in that case it is not

can we also have such value configurable for embedded_database ?

Describe the solution you'd like
A configurable value for embedded_database's pxc-root-password