Add terraform state registry (#36710)

Adds terraform/opentofu state registry with locking. Implements: https://github.com/go-gitea/gitea/issues/33644. I also checked [encrypted state](https://opentofu.org/docs/language/state/encryption), it works out of the box.

Docs PR: https://gitea.com/gitea/docs/pulls/357

---------

Co-authored-by: Andras Elso <elso.andras@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/packages/pkgspec/manager.go

@@ -0,0 +1,17 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package pkgspec
+
+import (
+	packages_model "code.gitea.io/gitea/models/packages"
+	packages_service "code.gitea.io/gitea/services/packages"
+	"code.gitea.io/gitea/services/packages/terraform"
+)
+
+func InitManager() error {
+	mgr := packages_service.GetSpecManager()
+	mgr.Add(packages_model.TypeTerraformState, &terraform.Specialization{})
+	// TODO: add more in the future, refactor the existing code to use this approach
+	return nil
+}