The previous commit gave the individual mounts more control over the
source and target properties. Do not require them at the global
schema but hand the control if they are optional over to the modules.
The order of entries in a dictionary is not specified by the JSON
standard and hard to control when marshalling dictionaries in Go.
Since the order of mounts is important and the wrong order leads
to wrong mount trees change the `mounts` field to an array. This
breaks existing manifests but after careful deliberation it was
concluded that the original schema with mounts as dictionaries
is not something we want to support. Apologies to everyone.
Adjust the schema of the copy and zipl stage accordingly.
Allows stages to access file systems provided by devices.
This makes mount handling transparent to the stages, i.e.
the individual stages do not need any code for different
file system types and the underlying devices.
A new host service that provides device functionality to stages.
Since stages run in a container and are restricted from creating
device nodes, all device handling is done in the main osbuild
process. Currently this is done with the help of APIs and RPC,
e.g. `LoopServer`. Device host services on the other hand allow
declaring devices in the manifest itself and then osbuild will
prepare all devices before running the stage. One desired effect
is that it makes device handling transparent to the stages, e.g.
they don't have to know about loopback devices, LVM or LUKS.
Another result is that specific device handling is now modular
like Inputs and Source are and thus moved out of osbuild itself.
