[SQLint] Be explicit when joining for `JOIN` keyword

[joe-re]

refer: https://about.gitlab.com/handbook/business-ops/data-team/platform/sql-style-guide/#joins

JOIN will work for INNER JOIN as default.

   -- Good
   FROM source
   JOIN other_source 
     ON source.id = other_source.id
   WHERE ...

   -- Bad
   FROM source
   LEFT JOIN other_source 
     ON other_source.id = source.id
   WHERE ...