config: create process.work_dir before box.cfg()

The `process.work_dir` option can be set in the configuration. All the
other directories/files has the before-box-cfg creation logic and it
seems meaningful to support it for `process.work_dir` too.

Part of #8862

NO_DOC=This change is too minor to describe in the documentation issue
       https://github.com/tarantool/doc/issues/3544. I'll work with the
       documentation team regarding details of startup/reload flow and
       we'll determine what should go to the user documentation and what
       shouldn't.