Add Prometheus for some Owncast metrics (#1744)

* Add Prometheus for some Owncast metrics. Closes #1303

* Wrap prometheus metrics endpoint in admin middleware

core/data/messages.go

@@ -35,3 +35,20 @@ func CreateMessagesTable(db *sql.DB) {
 		log.Fatal("error creating chat messages table", err)
 	}
 }
+
+// GetMessagesCount will return the number of messages in the database.
+func GetMessagesCount() int64 {
+	query := `SELECT COUNT(*) FROM messages`
+	rows, err := _db.Query(query)
+	if err != nil || rows.Err() != nil {
+		return 0
+	}
+	defer rows.Close()
+	var count int64
+	for rows.Next() {
+		if err := rows.Scan(&count); err != nil {
+			return 0
+		}
+	}
+	return count
+}