Missing HASTIC_SERVER_URL variable in docker-compose

[rozetko]

PR https://github.com/hastic/hastic-server/pull/931 introduced HASTIC_SERVER_URL variable to configure URL to bind websockets (default value is ws://localhost:8002). The problem is: the default value doesn't work in Docker because nothing outside the container can query container's localhost. We should add HASTIC_SERVER_URL to docker-compose.yml with default ws://server:8002 value