tests: workqueue tests overhaul adding new tests

During inspection of the workqueue tests, I find out testing gaps.
Decided to add new test cases that can improve Zephyr OS testing
quality.
Added new test cases:
1. test_work_item_supplied_with_func
In docs described that work item supplied with a handler function,
prove that it works.
2. test_process_work_items_fifo
Test that system process work items in first-in, first-out manner.
3. test_sched_delayed_work_item
Verify that delayed work item processed after specific period of time
stated by user.
4. test_workqueue_max_number
Test the limit of number of workqueues created
5. test_cancel_processed_work_item Created test to increase branch
coverage.

Modified existing test cases:
1. test_work_submit_handler updated Doxygen tag, added more detailed
description"

Signed-off-by: Maksim Masalski <maksim.masalski@intel.com>