Allowing flags to be passed via env variables or external files

[idomic]

We should do it explicitly, and then make sure we support an external file or an env variable so users don't have to repeat those multiple times.

Ref: ploomber/ploomber-engine#37

[edublancas]

I like how pytest does this: https://docs.pytest.org/en/7.1.x/example/simple.html

[idomic]

Yeah, that sounds like a common pattern we can embrace:

Either via an engine.ini

[ploomber-engine]
flags = -ra -q

Or via setting a shared env var:
export ENGINE_FLAGS="-v"

Or the existing command-line built in mechanism:
ploomber-engine input.ipynb output.ipynb --remove-tagged-cells some-tag

[edublancas]

Ok so I transferred this issue from ploomber-engine to core. We can implement the logic here to add it to other packages.

One thing I forgot to mention is that pytest supports multiple config files (there isn't a standard in the Python ecosystem, so I guess they decided to support them all)

https://docs.pytest.org/en/7.1.x/reference/customize.html

The most important ones are {package}.ini and pyproject.toml