pass CHARON_BEACON_NODE_HEADERS env var when set in .env file (#445)

closes #444

Author: nickh-obol

docker-compose.yml

@@ -91,6 +91,7 @@ services:
       - CHARON_BEACON_NODE_ENDPOINTS=${CHARON_BEACON_NODE_ENDPOINTS:-http://${CL:-lighthouse}:5052}
       - CHARON_BEACON_NODE_TIMEOUT=${CHARON_BEACON_NODE_TIMEOUT:-3s}
       - CHARON_BEACON_NODE_SUBMIT_TIMEOUT=${CHARON_BEACON_NODE_SUBMIT_TIMEOUT:-4s}
+      - CHARON_BEACON_NODE_HEADERS=${CHARON_BEACON_NODE_HEADERS:-}
       - CHARON_FALLBACK_BEACON_NODE_ENDPOINTS=${CHARON_FALLBACK_BEACON_NODE_ENDPOINTS:-}
       - CHARON_LOG_LEVEL=${CHARON_LOG_LEVEL:-info}
       - CHARON_LOG_FORMAT=${CHARON_LOG_FORMAT:-console}