Improve missing cluster ID guidance

[TangoEnSkai]

Summary

Improves the error shown when a remote DBUtils operation requires a cluster but no cluster ID is configured.

Fixes #51.

Why

The existing error says that cluster_id is required, but it does not tell users how to provide it. Users can otherwise miss the supported configuration argument and environment variable even though both are documented elsewhere.

What changed

Interface changes

None.

Behavioral changes

• The missing-cluster error now points users to Config(cluster_id="...") and DATABRICKS_CLUSTER_ID.

Internal changes

• Updated the existing DBUtils regression test to assert the actionable guidance.

How is this tested?

• uv run pytest tests/test_dbutils.py -q (19 passed)
• uv run ruff format --check databricks/sdk/dbutils.py tests/test_dbutils.py
• git diff --check

[github-actions]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger:
go/deco-tests-run/sdk-py

Inputs:

• PR number: 1545
• Commit SHA: 4ee33b4bb77da521e2ab4f2b546d715f82ee2605

Checks will be approved automatically on success.