Do a large chunk of the move to go

This commit moves a huge chunk of the code to go. The TODO.md document
indicates what is left to be done.

env/stack_self.go

@@ -0,0 +1,28 @@
+package env
+
+import "github.com/FAU-CDI/wisski-distillery/internal/stack"
+
+func (dis *Distillery) SelfStack() stack.Installable {
+	TARGET := "https://github.com/FAU-CDI/wisski-distillery"
+	if dis.Config.SelfRedirect != nil {
+		TARGET = dis.Config.SelfRedirect.String()
+	}
+
+	return dis.asCoreStack(stack.Installable{
+		Stack: stack.Stack{
+			Name: "self",
+		},
+
+		EnvFileContext: map[string]string{
+			"VIRTUAL_HOST":      dis.DefaultVirtualHost(),
+			"LETSENCRYPT_HOST":  dis.DefaultLetsencryptHost(),
+			"LETSENCRYPT_EMAIL": dis.Config.CertbotEmail,
+			"TARGET":            TARGET,
+			"OVERRIDES_FILE":    dis.Config.SelfOverridesFile,
+		},
+	})
+}
+
+func (dis *Distillery) SelfStackPath() string {
+	return dis.SelfStack().Dir
+}