Go: implement TTS for MiniMax provider and CLI testing for TTS (#14911)

### What problem does this PR solve?

This PR implement TTS for MiniMax provider and CLI testing for TTS

**The following functionalities are now supported:**

**MiniMax:**
- [x] Chat / Stream Chat 
- [x] Embedding
- [x] Rerank
- [x] Model listing
- [x] Provider connection checking
- [x] Text To Speech
- [ ] OCRFile
- [ ] ~~Audio To Text~~
- [ ] ~~Balance~~

**Verified examples from the CLI:**

```plaintext
RAGFlow(user)> tts with 'speech-2.8-hd@test@minimax' text 'He who desires but acts not, breeds pestilence.' play format 'wav' save './internal' param '{"voice_setting": {"voice_id": "English_radiant_girl", "speed": 1, "vol": 1, "pitch": 0}, "audio_setting": {"sample_rate": 32000, "bitrate": 128000, "format": "wav", "channel": 1}, "output_format": "hex"}'
Saved to directory: /home/infiniflow/Documents/development/ragflow/internal/speech-2.8-hd_output.wav
SUCCESS

RAGFlow(user)> stream tts with 'speech-2.8-hd@test@minimax' text 'He who desires but acts not, breeds pestilence.' play format 'wav' save './internal' param '{"voice_setting": {"voice_id": "English_radiant_girl", "speed": 1, "vol": 1, "pitch": 0}, "audio_setting": {"sample_rate": 32000, "bitrate": 128000, "format": "wav", "channel": 1}, "output_format": "hex"}'
Saved to directory: /home/infiniflow/Documents/development/ragflow/internal/speech-2.8-hd_output.wav
SUCCESS
```
Set `Play` to play audio in CLI
Set `Save` `PATH_TO_SAVE` to save file
Set `format` to save file in wav or mp3
Set `Param` align with official request body

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

internal/handler/providers.go

@@ -1166,14 +1166,12 @@ func (h *ProviderHandler) TranscribeAudio(c *gin.Context) {
 }
 
 type AudioSpeechRequest struct {
-	ProviderName *string  `json:"provider_name"`
-	InstanceName *string  `json:"instance_name"`
-	ModelName    *string  `json:"model_name"`
-	Text         *string  `json:"text"`
-	Language     []string `json:"language"`
-	Voice        int      `json:"voice"`
-	Stream       bool     `json:"stream"`
-	Volume       bool     `json:"volume"`
+	ProviderName *string           `json:"provider_name"`
+	InstanceName *string           `json:"instance_name"`
+	ModelName    *string           `json:"model_name"`
+	Text         *string           `json:"text"`
+	Stream       bool              `json:"stream"`
+	TTSConfig    *models.TTSConfig `json:"tts_config"`
 }
 
 func (h *ProviderHandler) AudioSpeech(c *gin.Context) {
@@ -1219,6 +1217,9 @@ func (h *ProviderHandler) AudioSpeech(c *gin.Context) {
 	}
 
 	ttsConfig := models.TTSConfig{}
+	if req.TTSConfig != nil {
+		ttsConfig = *req.TTSConfig
+	}
 
 	// Check if it's a stream request
 	if req.Stream {