replace magic number with named constant for logger flush delay

[ruslan0012]

Replace hardcoded 5 with LOGGER_FLUSH_DELAY_SECONDS constant in the application shutdown process. This
improves code readability and maintainability by making the logger flush timeout explicit and easily configurable.

The magic number was used only once in the codebase, making this a low-risk improvement that follows best practices for avoiding magic numbers in production code.