StackSets - Fix contract tests

[xiwhuang]

Issue #, if available:

Description of changes

1. Read handler returns FAILED operation with a NotFound error code for DELETED stacksets
2. Update/Delete handlers return FAILED operation with a NotFound error code for DELETED stacksets
3. Read handler returns StackSetName in resource model
4. Add input files
5. Add additionalProperties to fix warnings

Testing

collected 14 items                                                                                                                                                                                                                                                                 

handler_create.py::contract_create_delete PASSED                                                                                                                                                                                                                             [  7%]
handler_create.py::contract_create_duplicate SKIPPED (No writable identifiers. Skipping test.)                                                                                                                                                                               [ 14%]
handler_create.py::contract_create_read_success PASSED                                                                                                                                                                                                                       [ 21%]
handler_create.py::contract_create_list_success PASSED                                                                                                                                                                                                                       [ 28%]
handler_delete.py::contract_delete_read PASSED                                                                                                                                                                                                                               [ 35%]
handler_delete.py::contract_delete_list PASSED                                                                                                                                                                                                                               [ 42%]
handler_delete.py::contract_delete_update PASSED                                                                                                                                                                                                                             [ 50%]
handler_delete.py::contract_delete_delete PASSED                                                                                                                                                                                                                             [ 57%]
handler_delete.py::contract_delete_create SKIPPED (No writable identifiers. Skipping test.)                                                                                                                                                                                  [ 64%]
handler_misc.py::contract_check_asserts_work PASSED                                                                                                                                                                                                                          [ 71%]
handler_read.py::contract_read_without_create PASSED                                                                                                                                                                                                                         [ 78%]
handler_update.py::contract_update_read_success PASSED                                                                                                                                                                                                                       [ 85%]
handler_update.py::contract_update_list_success PASSED                                                                                                                                                                                                                       [ 92%]
handler_update_invalid.py::contract_update_non_existent_resource PASSED                                                                                                                                                                                                      [100%]

==================================================================================================================== 12 passed, 2 skipped in 598.39s (0:09:58) =====================================================================================================================

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