[dg] add check definitions command

[benpankow]

Summary

Introduces dg definitions validate, which calls the underlying dagster definitions validate with appropriate parameters for the current deployment or code location project. Largely cribbed from dg dev.

We could rename this to just dg validate or dg definitions-validate to avoid adding another top-level CLI.

dagster ~/repos/components_demo/my-deployment-2
$ dg definitions validate

Using ephemeral dagster definitions validate
2025-02-14 16:02:57 -0800 - dagster - INFO - Using temporary directory /Users/ben/repos/components_demo/my-deployment-2/tmpaxze6pxy for storage. This will be removed when dagster definitions validate exits.
2025-02-14 16:02:57 -0800 - dagster - INFO - To persist information across sessions, set the environment variable DAGSTER_HOME to a directory to use.
2025-02-14 16:02:58 -0800 - dagster.code_server - INFO - Starting Dagster code server for file /Users/ben/repos/components_demo/my-deployment-2/code_locations/analytics/analytics/definitions.py in process 55388
2025-02-14 16:02:58 -0800 - dagster - WARNING - /Users/ben/repos/components_demo/my-deployment-2/code_locations/analytics/.venv/lib/python3.12/site-packages/dagster/_core/utils.py:125: UserWarning: Found version mismatch between `dagster` (1.10.1) expected library version (0.26.1) and `dagster-sling` (1!0+dev).
  warnings.warn(message)

2025-02-14 16:02:58 -0800 - dagster.code_server - INFO - Started Dagster code server for file /Users/ben/repos/components_demo/my-deployment-2/code_locations/analytics/analytics/definitions.py in process 55388
2025-02-14 16:02:59 -0800 - dagster.code_server - INFO - Starting Dagster code server for file /Users/ben/repos/components_demo/my-deployment-2/code_locations/jaffle-platform/jaffle_platform/definitions.py in process 55392
2025-02-14 16:03:00 -0800 - dagster.code_server - INFO - Started Dagster code server for file /Users/ben/repos/components_demo/my-deployment-2/code_locations/jaffle-platform/jaffle_platform/definitions.py in process 55392
INFO:dagster.code_server:Started Dagster code server for file /Users/ben/repos/components_demo/my-deployment-2/code_locations/jaffle-platform/jaffle_platform/definitions.py in process 55392
2025-02-14 16:03:00 -0800 - dagster - INFO - Validation successful for code location analytics.
2025-02-14 16:03:00 -0800 - dagster - INFO - Validation successful for code location jaffle-platform.
2025-02-14 16:03:00 -0800 - dagster - INFO - All code locations passed validation.

There's also a fair amount of logspew on the dagster definitions validate end that a stacked PR can clean up.

Test Plan

Some brief test cases, tested manually.

[benpankow]

• [dg] add check definitions command #27873 👈 (View in Graphite)
• master

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[smackesey]

This is definitely functionality we want but I am strongly opposed to dg definitions validate as the name. Explained why in this doc which I posted in the channel and which touches on questions I'd like to settle before merging this: https://www.notion.so/dagster/Proposal-project-deployment-code-location-and-the-command-structure-of-dg-19c18b92e46280ad9d72e54cafdeec8e?pvs=4

Summary of that doc wrt this PR is that I think we should have a top-level check command and this should be dg check definitions (alongside dg check yaml).

[benpankow]

This is definitely functionality we want but I am strongly opposed to dg definitions validate as the name. Explained why in this doc which I posted in the channel and which touches on questions I'd like to settle before merging this: https://www.notion.so/dagster/Proposal-project-deployment-code-location-and-the-command-structure-of-dg-19c18b92e46280ad9d72e54cafdeec8e?pvs=4

Totally agree, I am unhappy with the command name as-written in this PR. Will wait for resolution on that doc.

[smackesey]

Can land this now as dg check definitions per discussion.