feat: connect to fail2ban db and extract total bad ips

Add dependencies on `sqlite` to allow connecting to the fail2ban database.
Add a new `db` module to handle all the database connections and data
queries used to generate metrics.
Export a new metric for the total number of bad IPs stored in the fail2ban
database.

db/db.go

@@ -0,0 +1,50 @@
+package db
+
+import (
+	"database/sql"
+	"log"
+	"strconv"
+)
+
+const queryCountTotalBadIps = "SELECT COUNT(1) FROM bips"
+
+type Fail2BanDB struct {
+	DatabasePath string
+	sqliteDB *sql.DB
+}
+
+func MustConnectToDb(databasePath string) *Fail2BanDB {
+	db, err := sql.Open("sqlite3", databasePath)
+	if err != nil {
+		log.Fatal(err)
+	}
+	return &Fail2BanDB{
+		DatabasePath: databasePath,
+		sqliteDB:     db,
+	}
+}
+
+func (db *Fail2BanDB) CountTotalBadIps() (int, error) {
+	stmt, err := db.sqliteDB.Prepare(queryCountTotalBadIps)
+	defer db.mustCloseStatement(stmt)
+
+	if err != nil {
+		return -1, err
+	}
+
+	result := ""
+	err = stmt.QueryRow().Scan(&result)
+
+	if err != nil {
+		return -1, err
+	}
+
+	return strconv.Atoi(result)
+}
+
+func (db *Fail2BanDB) mustCloseStatement(stmt *sql.Stmt) {
+	err := stmt.Close()
+	if err != nil {
+		log.Fatal(err)
+	}
+}