feat: add observoor role and ethereum_node addon

[qu0b]

Summary

• Add new observoor role for deploying the observoor eBPF agent as a Docker container
• Integrate observoor as an addon in the ethereum_node role via ethereum_node_observoor_enabled
• Observoor connects to the beacon node for slot timing, discovers Ethereum processes via host PID namespace, and attaches eBPF tracepoints at the kernel level to export aggregated metrics to ClickHouse

Role details

• Runs as a privileged container with pid_mode: host for process discovery and eBPF
• Mounts /sys/kernel/debug, /sys/fs/bpf, /proc, /sys/kernel/btf for kernel access
• Joins the shared Docker network so it can resolve the beacon container by name
• Config is templated with observoor_cl_endpoint, observoor_meta_client_name, observoor_meta_network_name, and ClickHouse settings

ethereum_node integration

• Addon file maps ethereum_node_cl_beacon_endpoint and ethereum_node_docker_networks
• Enable with ethereum_node_observoor_enabled: true

Test plan

• Deploy with ethereum_node_observoor_enabled: true against a running ethereum_node
• Verify observoor container starts and discovers EL/CL PIDs
• Verify beacon API connectivity (genesis fetch, sync polling)
• Verify ClickHouse export when configured
• Test cleanup path with ethereum_node_observoor_enabled: false