Since `tbl_cron` will contain a few rows (for now just 1),
cron list function call is not using any arguments.
This commit also remove cron http handler and endpoint.
The log level for the apps is using `log/slog` from Go standard library.
This commit change log format for fiber http logger to match with
the slog standard log format (date and time).
This commit also remove `APP_DEBUG` field from config struct.
TODO:
Use `slog` for default app output. Note that in this commit, the `slog`
output only implemented in `cron` "db migrate" and probe client.