Tox / Docker / Dependency updates

[nkemnitz]

Updating PyPI requirements.txt:

• remove superfluous dependencies:
  • urllib3
  • certifi
  • jsonschema
  • importlib-metadata
• document known dependency pins:
  • protobuf~=3.20
• remove likely outdated dependency pins - if still necessary, should document:
  • cloud-volume==6.1.1
  • task-queue==1.0.0
  • dracopy<=0.0.19
  • google-cloud-datastore>=1.8<=2.0dev
  • network==2.1
• add missing dependencies:
  • uwsgi
  • werkzeug

tox:

• switch to py3.11
• graph-tool now available as conda-forge package
• add tox-conda plugin + requirements.yml
• remove hacks previously added to link the tox environment to system dist-packages
• still requires installing conda and cbtemulator :/

Multi-stage Dockerfile:

• update .dockerignore to match .gitignore (+ .git/)
• build image for PyChunkedGraph dependencies in separate environment (including graph-tool)
• build image for Bigtable Emulator (gets rid off 1 GB Google Cloud SDK)
• adding shim for Bigtable Emulator call and pointing uwsgi to new Python environment

Fixes:

• When PCG internal checks already pre-filter columns, column_filter can end up as empty list. Bigtable however interprets this as "no filters applied". This PR changes behavior to raise an exception if an ambiguous, empty sequence is passed as column_filter, and fixes one such case captured by existing tests.

[fcollman]

@nkemnitz can i tag this version for a test deployment?