refs GW-232: GCS にアップロードできる

- 環境変数を configManager から取得

src/server/service/config-loader.js

@@ -220,6 +220,12 @@ const ENV_VAR_NAME_TO_CONFIG_INFO = {
     type:    TYPES.STRING,
     default: null,
   },
+  GCS_BUCKET: {
+    ns:      'crowi',
+    key:     'gsc:bucket',
+    type:    TYPES.STRING,
+    default: null,
+  },
 };
 
 class ConfigLoader {

src/server/service/file-uploader/gcp.js

@@ -10,7 +10,7 @@ module.exports = function(crowi) {
   const lib = new Uploader(configManager);
 
   function getGcsBucket() {
-    return process.env.GCS_BUCKET;
+    return configManager.getConfig('crowi', 'gsc:bucket');
   }
 
   function GCSFactory(isUploadable) {