refactor: correct import path for db_dialects package in mssql and postgres files; add db_dialects package

internal/app/db-wrapper/db_dialects/main.go

@@ -0,0 +1,7 @@
+package db_dialects
+
+const (
+	SqlServer string = "sqlserver"
+	Postgres  string = "postgres"
+	Null      string = "null"
+)