Add hello_orchestrator_py demo package

[bondada-a]

Summary

Adds hello_orchestrator_py - a minimal Python demo of the orchestrator pattern for dispatching JSON tasks to specialized MTC action servers.

Packages:

• hello_orchestrator_py - orchestrator server, print/move action servers, client
• hello_orchestrator_py_interfaces - action definitions

Architecture

                    ┌─────────────────┐
                    │  orchestrator   │
                    │     client      │
                    └────────┬────────┘
                             │ JSON task
                             ▼
                    ┌─────────────────┐
                    │  orchestrator   │
                    │     server      │
                    └────────┬────────┘
                             │
              ┌──────────────┴──────────────┐
              │                             │
              ▼                             ▼
     ┌─────────────────┐           ┌─────────────────┐
     │  print_server   │           │   move_server   │
     │  (logs message) │           │   (MTC motion)  │
     └─────────────────┘           └────────┬────────┘
                                            │
                                            ▼
                                   ┌─────────────────┐
                                   │     MoveIt      │
                                   │   (execution)   │
                                   └─────────────────┘

Base Action Server / Stages

Common patterns are extracted into base classes to avoid redundant code across action servers:

• BaseActionServer - All action servers share the same lifecycle (goal acceptance, execution, error handling).

• BaseStages - All MTC stages share the same initialization and plan-execute flow. Subclasses only implement task-specific logic.