i18n: enhance save_all_locales: false workflow

[marcuspollio]

When save_all_locales is set to false, users can disable output of content in selected non-default locales, by manually clicking the Disable (locale name) button in the three-dot menu in the top right corner of the Content Editor. This is a very handy feature.

However, when working on site with many languages/locales (more than 10), if users create new content and want to disable output of content for non-default locales, they need to manually perform the above steps for all non-default locales. This is not great UX.

The proposal here it to add an option to disable all non-default locales when creating new content, or enable only a specific subset of locales.

It could be a param such as: enable_new_content_locale: all | default | [en, fr, de] where all would be the current behavior (all locales are enabled by default), default would enable only the default_locale and a list of locales would enable the locales in this list and disable the others.

Does it make sense ? TIA