database start + cmake policy update

src/database_connection.cpp

@@ -0,0 +1,16 @@
+#include "../includes/database_service.hpp"
+#include <cstddef>
+
+
+DatabaseService& DatabaseService::getInstance(boost::asio::io_context &io_context, std::size_t pool_size) {
+    static DatabaseService INSTANCE;
+    return INSTANCE;
+}
+
+DatabaseService::DatabaseService(boost::asio::io_context& io_context, std::size_t pool_size) : io_context_(io_context), pool_size_(pool_size) {
+
+}
+
+DatabaseService::~DatabaseService() {
+
+}