Remove requirements.txt as a dependency (#1111)

* Remove requirements.txt as a dependency

This converts both docker and tox to use poetry, eliminating usage of
requirements.txt in both flows.

- In tox, uses the tox-poetry package which installs dependencies from
  the lockfile.
- In docker, uses
  https://stackoverflow.com/questions/53835198/integrating-python-poetry-with-docker
  as a reference.

* Don't copy pyproject.toml

* Remove obsoleted docs about requirements.txt

* Add --full-trace option to pytest

* Fix liccheck

liccheck works with requirements.txt, not with poetry, so there needs to
be an extra translation step.

* TEMP: Add WIP fix for pandas issue

This is just to see if the github actions would pass once this fix gets
merged, but it's being reviewed separately.

* Revert "TEMP: Add WIP fix for pandas issue"

This reverts commit 06e38e8cc77f5f3105c6e7a9449901db67aa1c82.

data/data-pipeline/pyproject.toml

@@ -36,6 +36,7 @@ pytest = "^6.2.4"
 safety = "^1.10.3"
 tox = "^3.24.0"
 pytest-mock = "^3.6.1"
+tox-poetry = "^0.4.1"
 
 [build-system]
 build-backend = "poetry.core.masonry.api"