Log Format Setting Storage

As a system administrator, I want to have the log format preference stored in the settings.json file, So that the configuration is centralized and can be deployed or audited across multiple installations.

Given the user changes the log format preference,
When the change is confirmed,
Then settings.json is updated with the new format key without altering any other existing settings.

Given the settings.json file is valid and contains the log format key,
When the application reads it at startup,
Then the correct serializer (JSON or XML) is instantiated and injected into the logging module.

Given any setting is modified (language, log format, or log location),
When it is saved,
Then the entire settings.json file remains valid and all other settings are preserved.