🚚(docker) make images naming consistent

It was quite confusing having development, production and
frontend images' names in the same Docker file. New comers
to the project would have some difficuluties when
differentiating frontend from backend images.

Try to make these naming more explicit and consistent.
Thanks @rouja for your recommendation.

Dockerfile

@@ -38,7 +38,7 @@ RUN yarn build
 
 
 # ---- Front-end image ----
-FROM nginxinc/nginx-unprivileged:1.25 as frontend
+FROM nginxinc/nginx-unprivileged:1.25 as frontend-production
 
 # Un-privileged user running the application
 ARG DOCKER_USER
@@ -147,7 +147,7 @@ WORKDIR /app
 ENTRYPOINT [ "/usr/local/bin/entrypoint" ]
 
 # ---- Development image ----
-FROM core as development
+FROM core as backend-development
 
 # Switch back to the root user to install development dependencies
 USER root:root
@@ -175,7 +175,7 @@ ENV DB_HOST=postgresql \
 CMD python manage.py runserver 0.0.0.0:8000
 
 # ---- Production image ----
-FROM core as production
+FROM core as backend-production
 
 ARG PEOPLE_STATIC_ROOT=/data/static