chore: Add debug_assemble binary

Attempt to reassemble messages produced by the mailbox state debug tool.
Unfortunately, most of it will only work if the messages have been fully
decrypted. To handle encrypted messages we need to have access to the
user's keyring, which is not available.

utils/debug/debug_assemble.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2023 Proton AG
+//
+// This file is part of Proton Mail Bridge.Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/ProtonMail/proton-bridge/v3/internal/user"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Printf("Usage: %v <dump dir>\n", os.Args[0])
+		return
+	}
+
+	if err := user.TryBuildDebugMessage(os.Args[1]); err != nil {
+		fmt.Printf("%v\n", err.Error())
+		return
+	}
+}