Steps to reproduce the problem described in #2634:

• Implement the SPI ReviewRequiredProvider in the module taskana-rest-spring-example-boot
• Put a break point in the reviewRequired method to stop the execution
• Start 2 instances of taskana-rest-spring-example-boot using PostgreSQL
• Open the GUI, select a task to complete it: the break point should kick in
• While the execution of one instance is paused, call the update task endpoint on the other instance (e.g. PUT http://localhost:8081/taskana/api/v1/tasks/:taskId) and change a custom field
• Using another break point, check the output of getTask() in TaskServiceImpl.requestReview: without the changes in this PR, the changes in the custom field from the update in the previous point should not be there

The explanation is that this last getTask() is returning cached data from the local SQL session.

By calling the new TaskanaEngine API method implemented in this PR from the SPI ReviewRequiredProvider, the cache is cleared and the last getTask() above returns fresh data from DB.

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