Build: migrate from pipenv to poetry

[roberta-dt]

Description

Moved from pipenv to poetry for Python dependency management, and upgraded the Python version to 3.9 ahead of Python 3.7 EOL

How has this been tested?

make commands tested manually
Automated tests all passing

Checklist

- [ ] I have commented my code, particularly in hard-to-understand areas

• I have successfully run the E2E tests
  - [ ] I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated any relevant documentation to reflect my changes
• I have assigned a reviewer and messaged them

[ghost]

Remember also to update the CI/CD pipelines in the cloudbuild directory to use a python:3.9 image

[ghost]

@roberta-dt you will also need to update the Makefile to change all the pipenv commands to poetry commands

[felix-datatonic]

/gcbrun

I'll review this PR instead.

[felix-datatonic]

Thanks a lot @roberta-dt for your contribution! Approved.

[ariadnafer]

/gcbrun