New:
- Added the WP CLI command `wp astra-sitest list` to list the demo sites.
- Added the WP CLI command `wp astra-sitest import <id>` to import the demo with ID.
- Added the WP CLI command `wp astra-sitest page_builder list` to list all page builders.
- Added the WP CLI command `wp astra-sitest page_builder set <slug>` to set the default page builder by page builder slug.