Support for export data as WXR (WordPress eXtended RSS)

[johanbove]

Is your feature request related to a problem? Please describe.

To allow existing users of Known sites to migrate their content to other platforms in a proper way Known could support the WXR format as an export target.

Describe the solution you'd like

From the "admin/export" screen users would be able to choose between RSS and WXR export format.

Describe alternatives you've considered

The current RSS export does not work well for moving a Known site to Micro.blog.

Additional context

• https://github.com/dllh/wp_scripts/blob/master/generate-wxr.php
• https://help.dreamhost.com/hc/en-us/articles/360050852091-Importing-and-exporting-a-WXR-file-in-WordPress