chore: Update treatment of required and side effect columns in config definitions

[johnnygreco]

required_columns and side_effect_columns for plugin column configurations are largely hidden because the abstract base class SingleColumnConfig has the default implementation returning an empty array for both of these properties. If the plugin you are writing depends on other columns or other plugins depend on the columns generated by your plugin, providing those column names through these two properties is essential. Failing to do so leads to errors at generation time that might be hard for a first-time plugin developer to debug.

• Option 1: We should have proper documentation on how to write plugins (must do).

• Option 2: Remove the default implementation of these properties from the base class and make it required for each extending class to provide implementations. The worst case here is that the plugin will need to return empty arrays, but most likely plugins will need to provide an implementation for at least one of these. Doing so will help developers catch errors in plugin development a lot sooner with straightforward fixes.