feat: Add persist option for MySQL and RabbitMQ

[yubingjiaocn]

Addressing - #205

[niallthomson]

Thanks for the PR @yubingjiaocn ! Only a minor comment across the storage class default value.

[niallthomson]

I believe that the convention is to set this to an empty string so that it uses the default storage class of the cluster.

[niallthomson]

I believe that the convention is to set this to an empty string so that it uses the default storage class of the cluster.

[niallthomson]

I believe that the convention is to set this to an empty string so that it uses the default storage class of the cluster.

[yubingjiaocn]

I commented the storageClass in values.yaml so it will use default storage class. If storageClass is set to empty string, no storage class or dynamic provisioning will be used.