Create article about passwords

The main goal of this page should be:

• describe that there is no default password and user sets password in the wizard, also describe the difference between Foris and system password
• describe how are these passwords stored and what encryption/hash function is used (/etc/shadow and /etc/config/foris auth.password)
• describe how to change the password (system and password for foris)

This should help meet the following mandatory requirements for Tier 1 defined by CSA Singapore's Cybersecurity Labeling Scheme

• 5.1-1:Where passwords are used and in any state other than the factory default, all consumer IoT devicepasswords shall be unique per device or defined by the user.
• 5.1-3:Authentication mechanisms used to authenticate users against a device shall use best practice cryptography, appropriate to the properties of the technology, risk, and usage.
• 5.1-4:Where a user can authenticate against a device, the device shall provide to the user or an administratora simple mechanism to changethe authentication value used.

Related to https://gitlab.nic.cz/turris/biz/singapore-certification/-/issues/1