'wdcli backup': Rework backup process

This commit reworks the backup process to dynamically find the list of
components.

internal/component/component.go

@@ -3,6 +3,7 @@ package component
 
 import (
 	"github.com/FAU-CDI/wisski-distillery/internal/config"
+	"github.com/tkw1536/goprogram/stream"
 )
 
 // Component represents a logical subsystem of the distillery.
@@ -31,20 +32,34 @@ type Component interface {
 	Base() *ComponentBase
 }
 
-// InstallableComponent implements an installable component
-type InstallableComponent interface {
+// Installable implements an installable component.
+type Installable interface {
 	Component
 
 	// Stack can be used to gain access to the "docker compose" stack.
 	//
-	// This should internally call
-	Stack() Installable
+	// This should internally call [ComponentBase.MakeStack]
+	Stack() StackWithResources
 
 	// Context returns a new InstallationContext to be used during installation from the command line.
 	// Typically this should just pass through the parent, but might perform other tasks.
 	Context(parent InstallationContext) InstallationContext
 }
 
+// Backupable represents a component with a Backup method
+type Backupable interface {
+	Component
+
+	// BackupName returns a new name to be used as an argument for path.
+	BackupName() string
+
+	// Backup backs up this component into the destination path path.
+	//
+	// The destination path may be a folder or directory, depending on the component.
+	// The destination path does not need to exist.
+	Backup(io stream.IOStream, path string) error
+}
+
 // ComponentBase implements base functionality for a component
 type ComponentBase struct {
 	Dir    string         // Dir is the directory this component lives in
@@ -67,7 +82,7 @@ func (ComponentBase) Context(parent InstallationContext) InstallationContext {
 }
 
 // MakeStack registers the Installable as a stack
-func (cb ComponentBase) MakeStack(stack Installable) Installable {
+func (cb ComponentBase) MakeStack(stack StackWithResources) StackWithResources {
 	stack.Dir = cb.Dir
 	return stack
 }