Add IsTemplate option in create repo ui and api (#12942)

Signed-off-by: a1012112796 <1012112796@qq.com>

Co-authored-by: Lauris BH <lauris@nix.lv>

models/repo.go

@@ -1083,6 +1083,7 @@ type CreateRepoOptions struct {
 	DefaultBranch  string
 	IsPrivate      bool
 	IsMirror       bool
+	IsTemplate     bool
 	AutoInit       bool
 	Status         RepositoryStatus
 	TrustModel     TrustModelType