Support .sql files in the importer

[bgrgicak]

The Playground plugin supports snapshot exports.

We need to ensure these snapshots work in Playground.

The main difference is that Playground uses wp-content/database/.ht.sqlite and that plugin uses wp-content/database/database.sql. These two exports are in different formats. Playground should detect if there is a SQL file and run it during import.

if both files are present, it should just load .ht.sqlite to prevent data overrides, or fail.

[bgrgicak]

We will need to implement passwordless login for this to work WordPress/playground-tools#219 (review)
After this is done the Playground plugin should be updated to use the import step WordPress/playground-tools#219 (review)

[flexseth]

*** unlinked to contributor day

[adamziel]

@flexseth this is a feature development problem, not a documentation problem.