Introduce slog-based structured logging throughout the booking service
and
server handlers. Add configurable log level via LOG_LEVEL environment
variable. Replace legacy log usage with slog and propagate logger to
booking service for improved observability.
* refactor return error when building booking service
* fix the description
* set taxable item by amount
* auto create tax items if the item is taxable
* fix linter
* remove legacy tax entry
* display multiple items
* use the price from the form
* improve item sorting
* lintfix
