fix(home-server): add default env values for secondary database

packages/home-server/.env.sample

@@ -9,3 +9,10 @@ PSEUDO_KEY_PARAMS_KEY=
 VALET_TOKEN_SECRET=
 
 FILES_SERVER_URL=
+
+SECONDARY_DB_ENABLED=false
+MONGO_HOST=localhost
+MONGO_PORT=27017
+MONGO_USERNAME=standardnotes
+MONGO_PASSWORD=standardnotes
+MONGO_DATABASE=standardnotes