add db connection, refactor code, add db migration files

cmd/api/logger.go

@@ -0,0 +1,10 @@
+package main
+
+import "log/slog"
+
+var StringToLogLevel = map[string]slog.Leveler{
+	"debug": slog.LevelDebug,
+	"info":  slog.LevelInfo,
+	"warn":  slog.LevelWarn,
+	"error": slog.LevelError,
+}