config: change working directory before the first `box.cfg()`

Paths in the configuration are specified relatively to process.work_dir, but the process enters that directory only inside the first box.cfg() call. Everything that runs earlier sees the startup directory instead (e.g. / under systemd), so the config module compensates by hand in several places (see #12610, #12928 and #13025).

We can chdir into process.work_dir right after the configuration collection, before any applier runs. The not-yet-chdir compensation code be dropped in that case. Only the very first config collection from sources and validation has to stay special.

Things to handle:

• Create a workdir before the chdir.
• Pass an absolute workdir to box.cfg() on startup and every reload (otherwise a relative path is applied twice and the non-dynamic check trips)
• Replace the type(box.cfg) predicates with an explicit flag or remove them

Note: the behavior change for early_load roles/app, whose relative fs paths become relative to workdir.

Trace the first configuration collection, validation, and applier sequence around box.cfg(), using the compensation cases referenced by #12610, #12928, and #13025. Check startup and reload handling, including early_load roles/apps and workdir creation. Done means relative paths resolve from process.work_dir, startup and reload pass an absolute workdir, and the existing type(box.cfg) predicates are no longer needed.