FEATURE: Add tasks to export and import site content (PR #12584)

Moving site settings, categories, tags, themes and theme components between sites is a difficult task and often cannot be automated. These script can be used to export to or import from a single zip archive all this content, without any users, topics, posts or other user generated content.


I like the concept behind this but am not sure about naming.


rake site:export_structure

rake site:import_structure

I also wonder how much fidelity we should provide here, should we prompt users during import asking them to confirm which parts to import? should we have any safeguards here for cases where a site is part populated?

Happy to merge this in when we agree on naming even prior to adding all the bells and whistles.

I am merging this, but I wonder if we should follow up with some tests here.

This is kind of dictating a format that we expect will remain stable, having a test will help document the format. Other tools except for export_structure may generate these files.