Adding local runner functionality for pytest and adding file existence test case

[taha-abdullah]

adding local runner functionality to pytest workflow:

• added new workflow 'pytest_local.yaml' to run pytest on a local runner
• added environment variables for subject directory and subject id

adding a new test to check for file existence in brainprint output

• added new pytest to check if all required files exist in the brainprint output
• removed comments from pytest_local.yaml

Notes:

• local runner needs to be provisioned on the repository with the necessary environment variables for this workflow to work

[taha-abdullah]

@kdiers requesting review

[kdiers]

Thanks for updating the tests and creating the runner file. We are still considering to have online / remote tests rather than local tests, so there might be further development. Still merging into the remove-freesurfer branch, and continuing development from there.