Add update XCom endpoint in RestAPI

[shubhamraj-git]

related: #45966

Debugging Airflow workflows often involves dealing with incorrect or missing XCom values, which can cause tasks to fail or behave unexpectedly.
Traditionally, fixing such issues requires rerunning tasks, modifying Dag logic, or even manually editing the Airflow metadata database—none of which are ideal in a production setting. With API-based XCom updates, users can quickly correct erroneous values without restarting entire workflows.
This is especially useful in long-running jobs, where reprocessing can be costly, or in dependency-heavy pipelines, where a single incorrect value can block multiple downstream tasks. By allowing targeted updates, this feature speeds up debugging, reduces downtime, and ensures smoother workflow execution.

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Steps to play around the feature.

Add the following Dag.

from datetime import datetime, timedelta
from airflow import DAG
from airflow.operators.python import PythonOperator
import time

def push_xcom_value(ti):
    value_to_push = "Hello from XCom!"
    ti.xcom_push(key='my_key', value=value_to_push)
    time.sleep(60)  # Wait for 1 minute, meanwhile you can update the XCom via API

def pull_xcom_value(ti):
    pulled_value = ti.xcom_pull(task_ids='push_task', key='my_key')
    print(f"Pulled Value: {pulled_value}") # Updated value should be present

default_args = {
    'owner': 'airflow',
    'catchup': False,
    'start_date': datetime(2024, 2, 5),
}

dag = DAG(
    'xcom_push_pull_dag',
    default_args=default_args,
    description='A simple DAG to demonstrate XCom push and pull',
    catchup=False,
)

push_task = PythonOperator(
    task_id='push_task',
    python_callable=push_xcom_value,
    dag=dag,
)

pull_task = PythonOperator(
    task_id='pull_task',
    python_callable=pull_xcom_value,
    dag=dag,
)

push_task >> pull_task

As soon as push_task has pushed to xcom, just update the value via API.
http://localhost:29091/docs#/XCom/update_xcom_entry

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