feat: add ManagementCommandExecutionRequested filter for observability

[ktyagiapphelix2u]

Summary

Adds a new ManagementCommandExecutionRequested filter to support observability
of Django management commands executed via manage.py in edx-platform.

This is part of a multi-repo effort to add Datadog monitoring around management
command execution using the Open edX Filters framework (OEP-50).

New Filter

Filter type: org.openedx.platform.management.command.execute.requested.v1

Location: openedx_filters/management/filters.py

Arguments passed through the pipeline:

• command_name (str): name of the management command being run
• service_variant (str): service variant, e.g. lms or cms
• command_runner (Callable): callable that executes the command — pipeline steps can wrap or replace this