Added the support for insert

tests/test_to_insert.cpp

@@ -0,0 +1,26 @@
+#include <gtest/gtest.h>
+
+#include <rfl/json.hpp>
+#include <sqlgen.hpp>
+#include <sqlgen/parsing/to_insert.hpp>
+
+namespace test_to_insert {
+
+struct TestTable {
+  std::string field1;
+  int32_t field2;
+  sqlgen::PrimaryKey<uint32_t> id;
+  std::optional<std::string> nullable;
+};
+
+TEST(general, test_to_insert) {
+  const auto insert_stmt = sqlgen::parsing::to_insert<TestTable>();
+
+  const std::string expected =
+      R"({"table":{"name":"TestTable"},"columns":["field1","field2","id","nullable"]})";
+
+  const auto json_str = rfl::json::write(insert_stmt);
+
+  EXPECT_EQ(json_str, expected);
+}
+}  // namespace test_to_insert