feat: install api python package inside docker

This mainly allow users to use the `funkwhale-manage` entrypoint.

api/Dockerfile

@@ -102,6 +102,9 @@ RUN apk add --no-cache \
 COPY . /app
 WORKDIR /app
 
+RUN set -eux; \
+  pip3 install --no-deps --editable .
+
 ENV CACHE_URL="redis://redis:6379/0"
 ENV CELERY_BROKER_URL="redis://redis:6379/0"
 

changes/changelog.d/install-api-python-package-in-docker.enhancement

@@ -0,0 +1 @@
+Install API python package in docker image