Require approval to run actions for fork pull request (#22803)

Currently, Gitea will run actions automatically which are triggered by
fork pull request. It's a security risk, people can create a PR and
modify the workflow yamls to execute a malicious script.

So we should require approval for first-time contributors, which is the
default strategy of a public repo on GitHub, see [Approving workflow
runs from public
forks](https://docs.github.com/en/actions/managing-workflow-runs/approving-workflow-runs-from-public-forks).

Current strategy:

- don't need approval if it's not a fork PR;
- always need approval if the user is restricted;
- don't need approval if the user can write;
- don't need approval if the user has been approved before;
- otherwise, need approval.

https://user-images.githubusercontent.com/9418365/217207121-badf50a8-826c-4425-bef1-d82d1979bc81.mov

GitHub has an option for that, you can see that at
`/<owner>/<repo>/settings/actions`, and we can support that later.

<img width="835" alt="image"
src="https://user-images.githubusercontent.com/9418365/217199990-2967e68b-e693-4e59-8186-ab33a1314a16.png">

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/migrations/migrations.go

@@ -19,6 +19,7 @@ import (
 	"code.gitea.io/gitea/models/migrations/v1_17"
 	"code.gitea.io/gitea/models/migrations/v1_18"
 	"code.gitea.io/gitea/models/migrations/v1_19"
+	"code.gitea.io/gitea/models/migrations/v1_20"
 	"code.gitea.io/gitea/models/migrations/v1_6"
 	"code.gitea.io/gitea/models/migrations/v1_7"
 	"code.gitea.io/gitea/models/migrations/v1_8"
@@ -463,6 +464,9 @@ var migrations = []Migration{
 	NewMigration("Add exclusive label", v1_19.AddExclusiveLabel),
 
 	// Gitea 1.19.0 ends at v244
+
+	// v244 -> v245
+	NewMigration("Add NeedApproval to actions tables", v1_20.AddNeedApprovalToActionRun),
 }
 
 // GetCurrentDBVersion returns the current db version

models/migrations/v1_20/v244.go

@@ -0,0 +1,22 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_20 //nolint
+
+import (
+	"xorm.io/xorm"
+)
+
+func AddNeedApprovalToActionRun(x *xorm.Engine) error {
+	/*
+		New index: TriggerUserID
+		New fields: NeedApproval, ApprovedBy
+	*/
+	type ActionRun struct {
+		TriggerUserID int64 `xorm:"index"`
+		NeedApproval  bool  // may need approval if it's a fork pull request
+		ApprovedBy    int64 `xorm:"index"` // who approved
+	}
+
+	return x.Sync(new(ActionRun))
+}