Method to download submission attachment (S3) urls from ODK Central

[Anuj-Gupta4]

Added and refactored submission related functionalities.

Test cases still need more work.

[spwoodcock]

I realised I made an error in the submission attachment URLs in my pyodk fork!

Original:

    _submission: str = "projects/{project_id}/forms/{form_id}/submissions/{{instance_id}}"
    list: str = f"{_submission}/attachments"
    get: str = f"{_submission}/attachments/{{fname}}"
    post: str = f"{_submission}/attachments/{{fname}}"
    delete: str = f"{_submission}/attachments/{{fname}}"

fixed:

    _submission: str = "projects/{project_id}/forms/{form_id}/submissions/{instance_id}"
    list: str = f"{_submission}/attachments"
    get: str = f"{_submission}/attachments/{{fname}}"
    post: str = f"{_submission}/attachments/{{fname}}"
    delete: str = f"{_submission}/attachments/{{fname}}"

The key here is that double curly braces are used in f-strings, but the _submission variable is not an f-string! I needed single braces for correct substitution. Without that fix, we always get 404 error when testing.

If you remove pyodk in this PR, then re-add it from source: https://github.com/hotosm/pyodk/tree/master-modified
then the functionality should all work 😄 (we can fix the pytest issues, and get this merged at some point 👍 )

[spwoodcock]

The functionality works, but the tests are quite complex and have issues.

It was suggested we merge for now to get integrating this into FMTM, then retroactively fix the tests 👍

[spwoodcock]

@Anuj-Gupta4 can I make a release based on this code do you think?

[Anuj-Gupta4]

I think the functionality itself is good to go. 👍