Added 'wav' and 'pcm' Audio Formats (#671)

* Added 'wav' and 'pcm' Audio Formats

Added "wav" and "pcm" audio formats as per OpenAI API documentation for createSpeech endpoint. 
Ref: https://platform.openai.com/docs/api-reference/audio/createSpeech
Supported formats are mp3, opus, aac, flac, wav, and pcm.

* Removed Extra Newline for Sanity Check

* fix: run goimports to get accepted by the linter

speech.go

@@ -33,6 +33,8 @@ const (
 	SpeechResponseFormatOpus SpeechResponseFormat = "opus"
 	SpeechResponseFormatAac  SpeechResponseFormat = "aac"
 	SpeechResponseFormatFlac SpeechResponseFormat = "flac"
+	SpeechResponseFormatWav  SpeechResponseFormat = "wav"
+	SpeechResponseFormatPcm  SpeechResponseFormat = "pcm"
 )
 
 var (