Serveral places with hardcoded UUIDs

## Describe the bug

ocis has still quite a few place where it using hardcoded UUIDs:

* as already mentioned the admin user (#3524) and the settings service user (#3343) use hardcoded UUIDs
* all the roles and permissions have hardcoded UUIDs https://github.com/owncloud/ocis/blob/master/extensions/settings/pkg/store/defaults/defaults.go
* the space id for the settings service is hardcoded https://github.com/owncloud/ocis/blob/master/extensions/settings/pkg/store/metadata/store.go#L23
* likely more (this is just what a quick glance revealed)

I think we need to address all of these to make sure the UUIDs we use are really globally unique (across instances)

cc @dragonchaser @C0rby @butonic @micbar