Added explicit OPA path to dockerfile (#216)

Author: danyi1212

Dockerfile

@@ -47,6 +47,7 @@ RUN apk update && \
 RUN mkdir /app/bin
 RUN chown -R permit:permit /app/bin
 COPY --from=opa_build --chmod=755 /opa /app/bin/opa
+ENV OPAL_INLINE_OPA_EXEC_PATH="/app/bin/opa"
 
 # bash is needed for ./start/sh script
 COPY scripts ./