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>

routers/api/v1/repo/repo.go

@@ -245,6 +245,7 @@ func CreateUserRepo(ctx *context.APIContext, owner *models.User, opt api.CreateR
 		AutoInit:      opt.AutoInit,
 		DefaultBranch: opt.DefaultBranch,
 		TrustModel:    models.ToTrustModel(opt.TrustModel),
+		IsTemplate:    opt.Template,
 	})
 	if err != nil {
 		if models.IsErrRepoAlreadyExist(err) {