Add close methods to all tasks

[markvai]

Issue: There is no option to free up resources used by a model, thus leadning to a a memory leak

Changes:

• Add a method that satisifies the closer interface to all tasks
• Done in the same way the method was added to "Text2Text"
• This allows for users that load the model to free up resources when finished.

[matteo-grella]

Thank you!