Instead of having a per-setting boolean to control whether it's visible
or hidden, there are now four values:
- `visible`: always show.
- `submission`: only show in the UI of a job submitter (like a Blender
add-on).
- `web`: only show in the web interface for management, but not when
submitting the job.
- `hidden`: never show; only available to the job compiler script as
internal setting.
Rename `pkg/api/flamenco-manager.yaml` to `flamenco-openapi.yaml`, to
distinguish the OpenAPI definition file from the Flamenco Manager
configuration file of the same name (but in a different directory).
No functional changes.
