Add deferrable mode to SFTPOperator

[sunildataengineer]

Description

The SFTPOperator currently runs in synchronous mode only, blocking
a worker slot for the entire duration of every file transfer.
For large file transfers, this wastes worker resources unnecessarily.

Proposed Solution
Add deferrable=True parameter to SFTPOperator following the same
pattern used in other Airflow providers. When deferrable=True,
the operator will defer execution to a trigger, freeing the worker
slot immediately and allowing the Triggerer to poll for completion.

Implementation Plan

• Add SFTPOperatorTrigger class in triggers/sftp.py
• Add deferrable param to SFTPOperator.init()
• Add defer() call in execute() when deferrable=True
• Add execute_complete() callback method
• Add unit tests

Related
Similar to deferrable mode already implemented in SFTPSensor.

I am willing to submit a PR for this.

Use case/motivation

No response

Related issues

No response

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[boring-cyborg]

Thanks for opening your first issue here! Be sure to follow the issue template! If you are willing to raise PR to address this issue please do so, no need to wait for approval.

[jroachgolf84]

@sunildataengineer, what sort of SFTP operations do you believe require deferrable execution?