[Documentation] Case Study: Use executorlib for task handling in a larger application

excutorlib can be integrated in existing frameworks and in combination with the flux framework is can provide an efficient task scaling solution, using the available resources while not oversubscribing them. Given the background of executorlib these tasks can be distributed on a high performance computing (HPC) cluster:

• Explain the use of external cache key in the resource dictionary: resource_dict={"cache_key": "foo"}. This enables external applications to define the key to store a given calculation in.
• Implement a check status function based on from executorlib import get_future_from_file as implemented in https://github.com/pyiron/executorlib/pull/915 . The external application uses its cache key to check the status of a given job object.
• Terminate a task which is no longer required using the from executorlib import terminate_task_in_cache function as implemented in https://github.com/pyiron/executorlib/pull/914 . The external application again uses its cache key to remove tasks from the backlog.

Start with the issue's referenced APIs, get_future_from_file and terminate_task_in_cache, and review the implementations in pull requests 915 and 914. Document a larger-application case study covering resource_dict={"cache_key": "foo"}, status checks, and task termination, with examples that show these workflows operating together.