Implement filesystem stores for pnd, device, sbi

.gitignore

controller/api/initialise_test.go

controller/config/config.go

controller/configs/containerlab-gosdn.toml.example

controller/configs/development-gosdn.toml.example

controller/interfaces/device/device.go

controller/northbound/server/pnd_test.go

controller/nucleus/device.go

controller/nucleus/deviceFilesystemStore.go

controller/nucleus/deviceFilesystemStore_test.go

controller/nucleus/deviceService.go

controller/nucleus/deviceStore.go

controller/nucleus/filesystem/filesystem-settings.go

controller/nucleus/memoryDeviceStore.go

controller/nucleus/memoryPndStore.go

controller/nucleus/pndFilesystemStore.go

controller/nucleus/pndFilesystemStore_test.go

controller/nucleus/pndStore.go

controller/nucleus/principalNetworkDomain_test.go

controller/nucleus/sbiFilesystemStore.go