Add EmptyOperator and decorator to decorators/empty.py

[AlefRP]

Add EmptyOperator with @task.empty decorator

Objective

This PR introduces a new operator called EmptyOperator with support for the @task.empty decorator. This operator serves as a placeholder for tasks in DAGs that do not have any execution logic but are useful for defining the structure of the workflow.

Key Changes

• Created airflow/decorators/empty.py with the implementation of EmptyOperator and the @task.empty decorator.
• Modified airflow/decorators/__init__.pyi to expose the new empty decorator.
• Added functionality to capture args/kwargs and log custom messages when executing tasks decorated with @task.empty.

Example Usage

from airflow.decorators import dag, task
from airflow.utils.dates import days_ago

@dag(schedule_interval=None, start_date=days_ago(1), catchup=False)
def my_empty_dag():
    @task.empty
    def start_task():
        print("This is a placeholder start task.")

    @task.empty
    def end_task():
        print("This is a placeholder end task.")

    start_task() >> end_task()

dag = my_empty_dag()

[boring-cyborg[bot]]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide (https://github.com/apache/airflow/blob/main/contributing-docs/README.rst) Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our pre-commits will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example DAG that shows how users should use it.
• Consider using Breeze environment for testing locally, it's a heavy docker but it ships with a working Airflow and a lot of integrations.
• Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
• Be sure to read the Airflow Coding style.
• Always keep your Pull Requests rebased, otherwise your build might fail due to changes not related to your commits. Apache Airflow is a community-driven project and together we are making it better 🚀. In case of doubts contact the developers at: Mailing List: dev@airflow.apache.org Slack: https://s.apache.org/airflow-slack

[eladkal]

Given that we plan to move decorators to standard provider https://github.com/apache/airflow/pull/44027 it's best to add new decorators to the standard provider directly rather than to the old path