fix: config naming and nesting

config/sample.engine.docker.yaml

config/sample.engine.yaml

src/aura_engine/base/config.py

src/aura_engine/core/channels.py

src/aura_engine/core/client.py

src/aura_engine/engine.py

src/aura_engine/plugins/monitor.py

src/aura_engine/scheduling/scheduler.py