az login --password-file

**Related command**
`az login`

**Is your feature request related to a problem? Please describe.**
As a bash user logging script output I do not want to inadvertently capture a secret in my logs. To use `az login` with a password I need to pass the password as an argument. This forces me to load the password into a shell variable which increases the likelihood the password will be captured in a log.

**Describe the solution you'd like**
I'd like `az login` to support an option `--password-file` which can be used instead of `--password`. The value will be a path to a file from which the password can be read.