Issue #3479185 by akulsaxena, joachim, smustgrave, mikelutz, quietone: Clarify...

 * Provides destination class for all content entities lacking a specific class.

 *

 * Available configuration keys:

 * - translations: (optional) Boolean, indicates if the entity is translatable,

 *   defaults to FALSE.

 * - translations: (optional) A boolean that indicates if the entity is

 *   translatable. When TRUE, migration rows will be considered as translations.

 *   This means the migration will attempt to load an existing entity and, if

 *   found, save the row data into it as a new translation rather than creating

 *   a new entity. For this functionality, the migration process definition must

 *   include mappings for the entity ID and the entity language field. If this

 *   property is TRUE, the migration will also have an additional destination ID

 *   for the language code.

 * - overwrite_properties: (optional) A list of properties that will be

 *   overwritten if an entity with the same ID already exists. Any properties

 *   that are not listed will not be overwritten.