support google gemini tts (#534)

* support google gemini tts

* wip

* wip

* wip

* wip

* wip

* support speech utils

lib/routes/api/speech-credentials.js

@@ -173,14 +173,23 @@ const encryptCredential = (obj) => {
   switch (vendor) {
     case 'google':
       assert(service_key, 'invalid json key: service_key is required');
+      let modified_service_key = service_key;
       try {
         const o = JSON.parse(service_key);
+        // support google gemini tts
+        if (model_id) {
+          o.model_id = model_id;
+        } else {
+          delete o.model_id;
+        }
+
         assert(o.client_email && o.private_key, 'invalid google service account key');
+        modified_service_key = JSON.stringify(o);
       }
       catch (err) {
         assert(false, 'invalid google service account key - not JSON');
       }
-      return encrypt(service_key);
+      return encrypt(modified_service_key);
 
     case 'aws':
       // AWS polly can work for 3 types of credentials:
@@ -582,7 +591,7 @@ router.put('/:sid', async(req, res) => {
           custom_tts_url,
           custom_tts_streaming_url,
           cobalt_server_uri,
-          model_id,
+          model_id: model_id !== undefined ? model_id : o.model_id,
           stt_model_id,
           voice_engine,
           options,
@@ -596,7 +605,8 @@ router.put('/:sid', async(req, res) => {
           resemble_tts_uri,
           resemble_tts_use_tls,
           api_uri,
-          houndify_server_uri
+          houndify_server_uri,
+          ...(vendor === 'google' && {service_key: JSON.stringify(o)})
         };
         logger.info({o, newCred}, 'updating speech credential with this new credential');
         obj.credential = encryptCredential(newCred);