remove: database-based metrics

Remove all database-based metrics from the metrics endpoint.
Remove all code related to pulling metrics from the fail2ban database.
Remove all configuration variables related to the fail2ban database.
The CLI parameter for the database path was not removed to avoid breaking
compatibility.
Update docker entrypoint to remove references to the fail2ban database.
Remove all references to the old database metrics from the README.

docker/run.sh

@@ -3,18 +3,11 @@
 # Print version to logs for debugging purposes
 /app/fail2ban-prometheus-exporter -version
 
-db_path=/app/fail2ban.sqlite3
 socket_path=/var/run/fail2ban/fail2ban.sock
 textfile_dir=/app/textfile/
 textfile_enabled=false
 
-# 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
+# Enable textfile metrics if the folder exists (i.e. was mounted by docker)
 if [ -d $textfile_dir ]; then
     textfile_enabled=true
 fi
@@ -22,7 +15,6 @@ fi
 # Start the exporter (use exec to support graceful shutdown)
 # Inspired by: https://akomljen.com/stopping-docker-containers-gracefully/
 exec /app/fail2ban-prometheus-exporter \
-    -db "$db_path" \
     -socket "$socket_path" \
     -collector.textfile=$textfile_enabled \
     -collector.textfile.directory="$textfile_dir"