Harmonize delegation and reassignment emails

There are currently 2 small issues with the delegation and reassignment emails

1) the comment is not built the same way for delegation and reassignment

• delegation use the user's comment : https://github.com/nuxeo/nuxeo/blob/release-10.10/nuxeo-features/nuxeo-platform-task/nuxeo-platform-task-core/src/main/java/org/nuxeo/ecm/platform/task/core/service/TaskServiceImpl.java#L595
• reassignment does not : https://github.com/nuxeo/nuxeo/blob/release-10.10/nuxeo-features/nuxeo-platform-task/nuxeo-platform-task-core/src/main/java/org/nuxeo/ecm/platform/task/core/service/TaskServiceImpl.java#L535

2) this information (comment and who did the delegation/reassignment) is missing for the body of the email whereas this information is important where you receive a notification that you were assigned to a task