Make admins adhere to branch protection rules (#32248)

This introduces a new flag `BlockAdminMergeOverride` on the branch
protection rules that prevents admins/repo owners from bypassing branch
protection rules and merging without approvals or failing status checks.

Fixes #17131

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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

services/forms/repo_form.go

@@ -219,6 +219,7 @@ type ProtectBranchForm struct {
 	RequireSignedCommits          bool
 	ProtectedFilePatterns         string
 	UnprotectedFilePatterns       string
+	BlockAdminMergeOverride       bool
 }
 
 // Validate validates the fields