[dg] Catch missing modules before running dg dev, dg check defs, dg list defs

[benpankow]

Summary

Runs a pre-flight check before invoking an underlying dagster or dagster-components command which requires loading a Python entrypoint module for a project. If that module is not accessible, raises a clearly actionable error:

dg list defs
Could not locate module `my_project_no_sync.definitions` using Python executable /Users/ben/.pyenv/versions/dagster/bin/python.

You may need to run `pip install -e /Users/ben/repos/components_demo/my_project_no_sync`.

How I Tested These Changes

New unit tests.

Changelog

[dg] dg CLI tools now more clearly error when the target project is not installed to the Python venv.

[benpankow]

• [dg] Catch missing modules before running dg dev, dg check defs, dg list defs #29511 👈 (View in Graphite)
• master

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[benpankow]

This doesn't feel great, a more robust option might be to move this to a really simple dagster-components CLI command.

[benpankow]

throwing back into draft to rearchitect a bit