Manifests-api: Added few tests related to manifests

Added the below tests:
* test_positive_create_1
* test_positive_delete_1
* test_negative_create_1
In this test, `cloned_manifest_path` is only used once. You can drop the `cloned_manifest_path = clone()` line entirely.

```python
task_id = entities.Organization(id=org_id).upload_manifest(
    path=clone()
)
```

If the above seems unclear, consider changing the import:

```python
task_id = entities.Organization(id=org_id).upload_manifest(
    path=manifests.clone()
)
```