### Description

Add listeners for Datasets (events)

### Use case/motivation

As Airflow administrators, we would like to trigger some external processes based on all datasets being created/updated by our users. We came across the listeners for the dag runs and task instances (which are also useful), but are still missing listeners for datasets.

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

"""
        Parse a given link, and verifies if it's a valid URL, or a 'mailto' link.
        Returns an iterator of invalid (owner, link) pairs.
        """
        for owner, link in self.owner_links.items():
            result = urlsplit(link)
            if result.scheme == "mailto":
                
                if not result.path:
                    yield result.path, link
            elif not result.scheme or not result.netloc:
                yield owner, link
class DagTag(Base):
    """A tag name per dag, to allow quick filtering in the DAG view."""
    __tablename__ = "dag_tag"
    name = Column(String(TAG_MAX_LEN), primary_key=True)
    dag_id = Column(
        StringID(),
        ForeignKey("dag.dag_id", name="dag_tag_dag_id_fkey", ondelete="CASCADE"),
        primary_key=True,
    )
    def __repr__(self):
        return self.name
class DagOwnerAttributes(Base):