Add MwaaServerlessDeleteWorkflowOperator

[kars0508]

Add a new operator to delete Amazon MWAA Serverless workflows.

What

• New MwaaServerlessDeleteWorkflowOperator with workflow_arn (required) and workflow_version (optional) parameters
• Follows existing patterns from other AWS delete operators (no if_not_found — lets ResourceNotFoundException propagate)

Motivation

Completes the CRUD operator set for MWAA Serverless workflows. Previously, the system test used a @task-decorated function with raw boto3 for cleanup — this replaces it with a proper operator.

Why a separate operator

Each MWAA Serverless API action maps to its own operator, matching the established pattern for the other operators in this module (Create, Update, Start, Stop).

Files changed

1. providers/amazon/src/airflow/providers/amazon/aws/operators/mwaa_serverless.py — new operator class
2. providers/amazon/tests/unit/amazon/aws/operators/test_mwaa_serverless.py — unit tests
3. providers/amazon/tests/system/amazon/aws/example_mwaa_serverless.py — system test updated to use the operator
4. providers/amazon/docs/operators/mwaa_serverless.rst — documentation

Testing

• Unit tests: all 18 pass locally
• System test: full end-to-end pass on Cloud Desktop (create → start → wait → update → start → stop → delete → cleanup)