feat: support reading fail2ban socket in docker

Update the docker container to support mounting the fail2ban server socket
and pointing the exporter at it. This allows the exporter to interact with
the socket from within the container.
The entire `/var/run` folder is mounted instead of just the socket file to
correctly handle fail2ban restarts (where the file will be deleted).

docker/run.sh

@@ -3,7 +3,19 @@
 # Print version to logs for debugging purposes
 /app/fail2ban-prometheus-exporter -version
 
+db_path=/app/fail2ban.sqlite3
+socket_path=/var/run/fail2ban/fail2ban.sock
+
+# Blank out the file paths if they do not exist - a hacky way to only use these files if they were mounted into the container.
+if [ ! -f "$db_path" ]; then
+    db_path=""
+fi
+if [ ! -S "$socket_path" ]; then
+    socket_path=""
+fi
+
 # Start the exporter (use exec to support graceful shutdown)
 # Inspired by: https://akomljen.com/stopping-docker-containers-gracefully/
 exec /app/fail2ban-prometheus-exporter \
-    -db /app/fail2ban.sqlite3
+    -db "$db_path" \
+    -socket "$socket_path"