Wheel problem while installing CKAN extension in docker

I am a newbie in CKAN and just installed CKAN with the [official docker compose setup](https://github.com/ckan/ckan-docker). It's now successfully running. Then I tried to install and activate the extensions ([ckanext-spatial](https://github.com/ckan/ckanext-spatial)). I downloaded the extensions git projects (with `git clone ...`) to the `.../ckan-docker/src` directory and inserted the plugins (`spatial_metadata` and `spatial_query`) in the `.env` file.

After start running the docker files with `docker compose -f ~/ckan-docker/docker-compose.dev.yml up` it breaks because the installation of required packages (pyproj and shapely) did not worked. I got following errors while building wheel for this package. I also tried it out by directly going into the docker container (`docker exec -it ckan /bin/bash`) and install these packages (`pip install ...`) but with the same result. I also tried to update/reinstall wheel.

So my question, why is there a problem with wheel and how can I solve this?

```
ckan | Collecting pyproj==3.4.1 (from -r /srv/app/src_extensions/ckanext-spatial/requirements.txt (line 9))
ckan | Using cached pyproj-3.4.1.tar.gz (217 kB)
ckan | Installing build dependencies: started
ckan | Installing build dependencies: finished with status 'done'
ckan | Getting requirements to build wheel: started
ckan | Getting requirements to build wheel: finished with status 'error'
ckan | error: subprocess-exited-with-error
ckan |
ckan | × Getting requirements to build wheel did not run successfully.
ckan | │ exit code: 1
ckan | ╰─> [2 lines of output]
ckan | :10: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
ckan | proj executable not found. Please set the PROJ_DIR variable. For more information see: https://pyproj4.github.io/pyproj/stable/installation.html
ckan | [end of output]
ckan |
ckan | note: This error originates from a subprocess, and is likely not a problem with pip.
ckan | error: subprocess-exited-with-error
ckan |
ckan | × Getting requirements to build wheel did not run successfully.
ckan | │ exit code: 1
ckan | ╰─> See above for output.
ckan |
ckan | note: This error originates from a subprocess, and is likely not a problem with pip.
```