Extension installs in Dockerfile.dev overridden

Hi,

While setting up a development environment using `docker-compose.dev.yml`, I noticed that extensions installed through pip in `Dockerfile.dev` won't be taken into account, because of
https://github.com/ckan/ckan-docker/blob/fc90a89227f432f58e7dcc80311dbeb1151ff90f/docker-compose.dev.yml#L32
I found this to be confusing. Is this intentional? Just removing the `home_dir` mounted volume solves the problem for me.
What is the correct way to run a CKAN Docker development setup that combines both extensions installed through the Dockerfile and an extension in development with local sources under `src`?

Thx!