Replaced deprecated apt-key, automated OS-based download

Dockerfile

@@ -2,16 +2,13 @@
 FROM debian:bullseye-slim
 
 # Install requirements
-RUN apt-get update && \
-    apt-get install -y gnupg
+RUN apt-get update && apt-get install -y gnupg
 
-# add the deb source
-# add the signing key
-# apt update
-# install the aprsc debian package
-RUN echo "deb http://aprsc-dist.he.fi/aprsc/apt bullseye main" > /etc/apt/sources.list.d/aprsc.list && \
-    gpg --keyserver keyserver.ubuntu.com --recv C51AA22389B5B74C3896EF3CA72A581E657A2B8D && \
-    gpg --export C51AA22389B5B74C3896EF3CA72A581E657A2B8D | apt-key add - && \
+# add signing key and deb source, install aprsc
+RUN gpg --keyserver keyserver.ubuntu.com --recv-keys C51AA22389B5B74C3896EF3CA72A581E657A2B8D && \
+    gpg --export C51AA22389B5B74C3896EF3CA72A581E657A2B8D > /etc/apt/trusted.gpg.d/aprsc.gpg && \
+    chown root:root /etc/apt/trusted.gpg.d/aprsc.gpg && chmod 644 /etc/apt/trusted.gpg.d/aprsc.gpg && \
+    echo "deb [signed-by=/etc/apt/trusted.gpg.d/aprsc.gpg] http://aprsc-dist.he.fi/aprsc/apt $(cat /etc/os-release | grep VERSION_CODENAME | awk '{gsub("VERSION_CODENAME=", "");print}') main" > /etc/apt/sources.list.d/aprsc.list && \
     apt-get update && \
     apt-get install -y aprsc