CI: better logic to choose package manager

wopiserver.Dockerfile

@@ -14,10 +14,12 @@ LABEL maintainer="cernbox-admins@cern.ch" \
 # prerequisites: we explicitly install g++ as it is required by grpcio but missing from its dependencies
 WORKDIR /app
 COPY requirements.txt .
-RUN if [ '$BASEIMAGE' = 'python:3.10-slim-buster' ]; then \
- apt -y install g++; \
+RUN if command -v apt &> /dev/null; then \
+ echo "Using apt"; apt -y install g++; \
+ elif command -v apk &> /dev/null; then \
+ echo "Using apk"; apk add g++; \
  else \
- apk add g++; \
+ echo "This distribution does not provide a supported package manager"; false; \
  fi
 RUN pip3 install --upgrade pip setuptools && \
  pip3 install --no-cache-dir --upgrade -r requirements.txt