Define a good approach to manage password in terraform

As we mentioned here: https://github.com/Greenstand/treetracker-infrastructure/issues/202 there are some problem with managing the password:

The password generated by terraform can not display in the digital ocean panel
Because of above, we can not check the password easyly, now, we need to download the state file to check the password in plaint text
Storing the password in the state isn't so safe, once we ruined the state file by accident, then, we lost all those password, and every clients connecting to db need to reset the password, we need to do some research to see if there is some way that we can save vault text in git and read it in terraform.

Greenstand / treetracker-infrastructure