build: Migrate to Poetry
Poetry is starting to be the standard used for the rest of Toolforge
infrastructure written in Python, and the lock file is a nice feature
for a fully containerized app. This commit migrates the app to use
Poetry. Dependencies are pinned to the currently running versions and a
follow-up will upgrade them.
Bug: T354751
Related MRs:
- !54 (merged)
- !53 (merged) (This MR)
- !55 (merged)
- main