Updated naming convention regarding result_sample.py in service development

[jasper-vdhoven]

Reason for pull request:

Within the docs for creating a new service there is reference to result_sample.py:

Service Python code
In your service directory, you will first start by creating your service's python file. Let's use result_sample.py.
Put the following code in your service's file:

Build your first service

Afterwards, this same file is referenced as sample.py in the section on how to run your service:

From a terminal, run the run_service_once module, specifying the service path for the service to run and the path to the file to scan. For this example, we will have the service scan itself.

python -m assemblyline_v4_service.dev.run_service_once sample.Sample sample.py\

The run_service_once module creates a directory at the same spot where the file is found with the service name that scanned the file appended to it. In the previous example, the output of the service should be located at ~/git/services/assemblyline-service-sample/sample.py_sample. The directory will contain a result.json file containing the result from the service.

[Run your service](https://cybercentrecanada.github.io/assemblyline4_docs/developer_manual/services/run_your_service/#standalone-mode

When following the exact commands offered within the step-by-step, the execution will fail as there is no sample.py for this newly created service:

(venv) user@assemblyline:~/deployments/services/assemblyline-service-sample$ python -m assemblyline_v4_service.dev.run_service_once sample.Sample sample.py
Could not find service in path. Check your environment variables.
Traceback (most recent call last):
  File "/usr/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/user/deployments/alv4/assemblyline-v4-service/assemblyline_v4_service/dev/run_service_once.py", line 250, in <module>
    rs.try_run()
  File "/home/user/deployments/alv4/assemblyline-v4-service/assemblyline_v4_service/dev/run_service_once.py", line 35, in try_run
    self.service_class = load_module_by_path(SERVICE_PATH)
  File "/home/user/deployments/alv4/assemblyline-base/assemblyline/common/importing.py", line 12, in load_module_by_path
    module = importlib.import_module(module_path)
  File "/usr/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 984, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'sample'

Suggestion

I would like to suggest to adopt either the use of sample.py throughout the services example, or stick with result_sample.py as is proposed through this PR.

[cccs-kevin]

Thank you!