Make openaiModelMapper optional in the init process

Modify the initialization condition in `azure/init.go` to allow the
`openaiModelMapper` environment variable to be optional. This change
facilitates configurations where the model mapper is not needed, and
improving flexibility.

Resolves: #95

azure/init.go

@@ -31,7 +31,7 @@ func Init() error {
 	apiVersion = viper.GetString(constant.ENV_AZURE_OPENAI_API_VER)
 	endpoint = viper.GetString(constant.ENV_AZURE_OPENAI_ENDPOINT)
 	openaiModelMapper = viper.GetString(constant.ENV_AZURE_OPENAI_MODEL_MAPPER)
-	if endpoint != "" && openaiModelMapper != "" {
+	if endpoint != "" {
 		if apiVersion == "" {
 			apiVersion = "2023-07-01-preview"
 		}