Add bundle_name attribute to DAG and update PythonDagImporter to set it

[bramhanandlingala]

What

Add a bundle_name attribute to DAG objects and populate it when DAGs are imported from a bundle.

Why

This makes it possible to identify which DAG bundle a DAG originated from and enables bundle-specific DAG policies.

Example:

@hookimpl
def dag_policy(dag):
    if dag.bundle_name == "example_dags":
        return

    if dag.bundle_name == "special_dags":
        ...

Changes

• Added bundle_name field to DAG.
• Set dag.bundle_name during DAG import.
• Added tests to verify imported DAGs receive the configured bundle name.

Fixes #68575

[jroachgolf84]

@bramhanandlingala - I've already opened a PR for this issue, and it was assigned to me. Please feel free to provide a review on it, but no need to duplicate work :)

#68583

[bramhanandlingala]

@jroachgolf84 , Thanks for the heads-up. I wasn't aware there was already an assigned PR for this issue. I'll close my PR to avoid duplicating work and will review #68583 instead. Appreciate the clarification!