Support yaml for addResourceBundle

[libasoles]

I'm using yaml on init method, like this:

backend: {
      loadPath: path.join(__dirname, '/../locales/{{lng}}/{{ns}}.yml'),
    },

Afterwards, I want to load more resources, but addResourceBundle doesn't recognize yaml format. It doesn't fail, it just wont's load the needed translations.

[jamuhl]

addResourceBundle will add a json object

just call loadNamespaces to load additional ns: https://www.i18next.com/overview/api#loadnamespaces