Fix error handling in the database query module

Changes in this merge request

• Add proper error handling in libs/db/query_exec. Uses a catch function after each then to proper capture database errors and report them to the user.
• Add logging the error stack when a database query error occurs.
• Change error message reported in the response when a database query occurs, because the user making the request does not need to know about an internal database error.

Temos algum teste para isso? Mudei um SQL para verificar na minha máquina, mas seria interessante um teste específico para esse middleware

mentioned in commit 8b78356e

merged