feat(invoice): add send route

internal/email/model.go

@@ -0,0 +1,17 @@
+package email
+
+import "io"
+
+type Mail struct {
+	To          []string
+	Cc          []string
+	Bcc         []string
+	Subject     string
+	Body        string
+	Attachments []Attachment
+}
+type Attachment struct {
+	Name     string
+	MimeType string
+	Content  io.Reader
+}