zulip lib: Initialize pyproject.toml for Poetry.

[rht]

Still missing:

• there is currently no way to specify data_files for the integrations/ folder to be copied to share/zulip (see

  python-zulip-api/zulip/setup.py

  Line 56 in 31365a8

  data_files=list(recur_expand("share/zulip", "integrations")),

  ). Relevant Poetry issue: Support for data_files python-poetry/poetry#890.
• since pyproject.toml is declarative, I can't add a function for it to read __version__ from zulip/__init__.py. But someone had already implemented a plugin

[rht]

Someone made a Poetry plugin for data_files: python-poetry/poetry#890 (comment). As such, both issues have an unofficial solution. But it looks like there won't be any official solution any time soon (the issue I linked got closed anyway).

Should I close this PR and consider using Poetry to be a no-go?