Hash passwords for the local-file auth provider

[mountaindude]

Is your feature request related to a problem? Please describe.
As of v1.0.0 the passwords for the local-file auth provider are stored in clear text in a YAML file on disk.

This is not good at all from a security point of view.
Better would be to store a hashed and salted version of the passwords in the YAML file.

Describe the solution you'd like
Add an option to the local-file auth provider in the main YAML config file.
Something like:

localFile:                          # "Local file" provider reads user data from a file on disk
    enable: false
    hashPassword: true
    url: https://<FQDN>:8081        # URL where login UI for this provider is available
    userDirectory: lab              # Qlik Sense user directory that will be used for the authenticated user
    userFile: ./config/users.yaml   # YAML file containing usernames and passwords

The default (if the hashPassword field is not specified) would be to require hashed passwords.
If someone really don't want hashed passwords they can set the field to false.

NOTE: This would be a breaking change as the default as of version 1.0 is that passwords are NOT hashed.

Use an established, proven hashing library instead of inventing something new.