Adds password rotation for databases

[digiserg]

This feature implements a new option to add a list of databases (MySQL, Cassandra or Postgres) to sync down credentials. This is intended for password rotation:

• Admin changes password on secrets store backend (Vault, AWS, Google, etc)
• Credentials are synced down and converted into a Kubernetes secret used by the applications
• Database is updated with the new password
• Applications re-read secret and continue operations

Please be aware your application must be coded in a way it will support password rotation.