Fix temperature not being set to 0 due to json omitempty

The issue was caused by the `omitempty` tag in the Go struct, which prevented the `temperature` field from being included in the JSON output when it was set to 0.

Signed-off-by: Butui Hu <hot123tea123@gmail.com>

relay/channel/palm/dto.go

@@ -18,7 +18,7 @@ type PaLMPrompt struct {
 
 type PaLMChatRequest struct {
 	Prompt         PaLMPrompt `json:"prompt"`
-	Temperature    float64    `json:"temperature,omitempty"`
+	Temperature    *float64   `json:"temperature,omitempty"`
 	CandidateCount int        `json:"candidateCount,omitempty"`
 	TopP           float64    `json:"topP,omitempty"`
 	TopK           uint       `json:"topK,omitempty"`