Add attachment support for code review comments (#29220)

Fixes #27960, #24411, #12183

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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/forms/repo_form.go

@@ -626,6 +626,7 @@ type CodeCommentForm struct {
 	SingleReview   bool   `form:"single_review"`
 	Reply          int64  `form:"reply"`
 	LatestCommitID string
+	Files          []string
 }
 
 // Validate validates the fields