Obfuscate passwords

[rgstephens]

Database passwords are written to the log when verbose logging is enabled.

Rasa version: 1.9.5

Issue:
Passwords should not be written in clear text to the log.

[akelad]

@rgstephens do you have details of where the passwords get logged? As in, at which stage of the start up?

[rgstephens]

Here's an example log message (I've replaced the password with asterisks):

DEBUG    rasa.core.tracker_store  - Attempting to connect to database via 'postgresql://admin:****************@db:5432/rasa'

[ncplol]

This looks pretty simple, I can open a PR as a first contribution. Wondering if/how it makes sense to test for this?