feat: add opt-in Optimum Gateway compose overlay

[swarna1101]

Summary

Adds an opt-in Optimum Gateway service on the dvnode network so the beacon node can receive blocks earlier via Optimum’s mesh.

• Off by default: default COMPOSE_FILE is unchanged. Enable by appending :compose-optimum.yml.
• No changes to Charon, VC, DV keys, or CL command:.
• Gateway is configured as a direct libp2p peer of the CL (init-optimum.sh writes direct_cl_peers from GET /eth/v1/node/identity).
• Image: getoptimum/gateway:v1.1.1. API key via OPT_API_KEY; cluster id via GATEWAY_CLUSTER_ID (Optimum cluster, not CLUSTER_NAME).
• CL P2P on dvnode: 9000 for Lighthouse/Lodestar/Teku/Nimbus/Grandine; 13000 for Prysm.

Enable / disable: optimum/README.md.

Validated on Hoodi (Approach A, Lighthouse) against a live DV: getoptimum/optimum-gateway#25

Test plan

• Stock CDVN (no overlay in COMPOSE_FILE) does not start optimum-gateway
• With overlay: ./optimum/init-optimum.sh then docker compose up -d optimum-gateway
• curl localhost:48123/health -> cl_peers >= 1
• Remove :compose-optimum.yml -> stock behaviour restored

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[swarna1101]

@KaloyanTanev can you pls review this