Docker and symlink to backend

I have yii2 project on which i use backend at my examplesite.com/admin

i need to create a symlink in my local environment from projectname/frantend/web/admin to projectname/backend/web

How can i accomplish this on docker? i ve been able to run a

ln -s /projectfile/backend/web/ admin

within the container, but not during container build.

Is there any way through Dockerfile or docker-compose to accomplish that?