Add password hash authentication method

[spacefrogg]

This is an update of the previous attempt to bring purely user-controlled hash-based authentication to hyprlock.

It is based on #585 and brings a hyprlock-pwhash helper binary to create the right hash config in the right location. The location of the hash config file can be chosen via the auth:sodium:secret_file config option and the --config option to hyprlock-pwhash.

The auth:sodium:secret_file config option can be:

1. a stem which gets completed to "main config file location" + OPT + ".conf"
2. a relative path (with at least ./... one slash) which gets extended to "main config file location" + OPT
3. an absolute path that is taken as is.

To be conservative, the PAM and sodium authentication methods are mutually exclusive. That may be unnecessary.

Closes #573