Enable plugins per demo

[bburda]

Summary

Configure and enable gateway plugins in each demo with appropriate plugin allocation.

Motivation

Gateway v0.4.0 has a rich plugin ecosystem. Each demo should showcase relevant plugins.

Proposed solution

All demos:

• Enable linux introspection plugin (procfs, systemd, container) - shows process-level diagnostics
• Enable graph provider plugin

sensor_diagnostics only:

• Enable topic_beacon and param_beacon plugins
• Add beacon topic publishers to sensor nodes for push-based entity enrichment

turtlebot3 and moveit:

• Linux introspection + graph provider only (manifests handle discovery)

Update medkit_params.yaml for each demo with plugin configuration.

Acceptance criteria

• Plugins load in all demos
• Linux introspection data visible via API per entity
• Beacons working in sensor demo (entity has beacon metadata)