Include References: <Message-ID of triggering e-mail>, if any, in the comment notification

This mirrors the ticket_new notification

api/graph/schema.graphqls

@@ -770,6 +770,7 @@ input SubmitCommentEmailInput {
   cmd: EmailCmd
   resolution: TicketResolution
   labelIds: [Int!]
+  messageId: String!
 }
 
 """

api/graph/schema.resolvers.go

@@ -1243,6 +1243,8 @@ func (r *mutationResolver) SubmitCommentEmail(ctx context.Context, trackerID int
 		}
 		builder.InsertNotifications(event.ID, &commentID)
 
+		builder.InReplyTo(&input.MessageID)
+
 		conf := config.ForContext(ctx)
 		origin := config.GetOrigin(conf, "todo.sr.ht", true)
 		details := SubmitCommentDetails{

todosrht-lmtp

@@ -177,6 +177,7 @@ class MailHandler:
         input = {
             "text": body,
             "senderId": sender.id,
+            "messageId": mail["Message-ID"].removeprefix("<").removesuffix(">"),
         }
 
         cmds = ["!resolve", "!resolved", "!reopen"]