In Docker, set JAVA_OPTS instead of FINERACT_TENANTS_URL.
Because ARG/ENV in the Dockerfile can't (easily) be changed at run-time.
At first I tried to override the ENTRYPOINT with a script which sets
JAVA_OPTS based on FINERACT_TENANTS_URL and then delegates to the original
/app-entrypoint.sh; that didn't immediately work, so this seems simpler.
Including make default tenant JDBC hostname & port configurable at Docker container run instead of build time.