common: restore default disk backup behaviour

In testing it was observed that the upstream disk API changes are excluding disks from Proxmox backup jobs by default (setting backup=0).
This commit reinstates the behaviour of previous versions of this packer-plugin-proxmox where disks created by Packer are enabled for backup by default.
A new ExcludeFromBackup disk field has been added to opt out of this behaviour.

.web-docs/components/builder/clone/README.md

@@ -447,6 +447,9 @@ Example:
 - `asyncio` (string) - Configure Asynchronous I/O. Can be `native`, `threads`, or `io_uring`.
   Defaults to io_uring.
 
+- `exclude_from_backup` (bool) - Exclude disk from Proxmox backup jobs
+  Defaults to false.
+
 - `discard` (bool) - Relay TRIM commands to the underlying storage. Defaults
   to false. See the
   [Proxmox documentation](https://pve.proxmox.com/pve-docs/pve-admin-guide.html#qm_hard_disk_discard)

.web-docs/components/builder/iso/README.md

@@ -587,6 +587,9 @@ Example:
 - `asyncio` (string) - Configure Asynchronous I/O. Can be `native`, `threads`, or `io_uring`.
   Defaults to io_uring.
 
+- `exclude_from_backup` (bool) - Exclude disk from Proxmox backup jobs
+  Defaults to false.
+
 - `discard` (bool) - Relay TRIM commands to the underlying storage. Defaults
   to false. See the
   [Proxmox documentation](https://pve.proxmox.com/pve-docs/pve-admin-guide.html#qm_hard_disk_discard)

builder/proxmox/common/config.go

@@ -362,6 +362,9 @@ type diskConfig struct {
 	// Configure Asynchronous I/O. Can be `native`, `threads`, or `io_uring`.
 	// Defaults to io_uring.
 	AsyncIO string `mapstructure:"asyncio"`
+	// Exclude disk from Proxmox backup jobs
+	// Defaults to false.
+	ExcludeFromBackup bool `mapstructure:"exclude_from_backup"`
 	// Relay TRIM commands to the underlying storage. Defaults
 	// to false. See the
 	// [Proxmox documentation](https://pve.proxmox.com/pve-docs/pve-admin-guide.html#qm_hard_disk_discard)

builder/proxmox/common/step_start_vm.go

@@ -299,6 +299,10 @@ func generateProxmoxDisks(disks []diskConfig, isos []ISOsConfig, cloneSourceDisk
 		case "K":
 			size = proxmox.QemuDiskSize(tmpSize)
 		}
+		backup := true
+		if disks[idx].ExcludeFromBackup {
+			backup = false
+		}
 
 		switch disks[idx].Type {
 		case "ide":
@@ -311,6 +315,7 @@ func generateProxmoxDisks(disks []diskConfig, isos []ISOsConfig, cloneSourceDisk
 					Format:          proxmox.QemuDiskFormat(disks[idx].DiskFormat),
 					Discard:         disks[idx].Discard,
 					EmulateSSD:      disks[idx].SSD,
+					Backup:          backup,
 				},
 			}
 			for {
@@ -371,6 +376,7 @@ func generateProxmoxDisks(disks []diskConfig, isos []ISOsConfig, cloneSourceDisk
 					Discard:         disks[idx].Discard,
 					EmulateSSD:      disks[idx].SSD,
 					IOThread:        disks[idx].IOThread,
+					Backup:          backup,
 				},
 			}
 			for {
@@ -400,6 +406,7 @@ func generateProxmoxDisks(disks []diskConfig, isos []ISOsConfig, cloneSourceDisk
 					Format:          proxmox.QemuDiskFormat(disks[idx].DiskFormat),
 					Discard:         disks[idx].Discard,
 					EmulateSSD:      disks[idx].SSD,
+					Backup:          backup,
 				},
 			}
 			for {
@@ -429,6 +436,7 @@ func generateProxmoxDisks(disks []diskConfig, isos []ISOsConfig, cloneSourceDisk
 					Format:          proxmox.QemuDiskFormat(disks[idx].DiskFormat),
 					Discard:         disks[idx].Discard,
 					IOThread:        disks[idx].IOThread,
+					Backup:          backup,
 				},
 			}
 			for {