fixes matomo-org/plugin-QueuedTracking#21

Plugin settings are configured in the UI under "Administration => Plugin Settings". However, sometimes one might want to define a different config value on different servers (for example in a load balanced environment) see for example matomo-org/plugin-QueuedTracking#21

For example one might want to enabled QueuedTracking on one server, but disable it on another and use log importer instead on the other server.

To overwrite a plugin system setting specify the plugin name and plugin setting name in the config/config.ini.php file like this:

[PluginName]
pluginSettingName = pluginSettingValue

Actual example for plugin QueuedTracking:

[QueuedTracking]
processDuringTrackingRequest = 0
queueEnabled = 1

Important:

• Setting names are case sensitive
• Once a plugin setting is configured in the config file, the value can be no longer changed in the UI since we cannot modify the config file eg in a load balanced environment etc. A side effect of this is to being able to hide specific system settings for users by specifying them in the config
• In another pull request we will offer the possibility to see a all configured config values, and also to see all available plugin names + plugin system setting names that can be configured including documentation