Filters the site data before the get_sites query takes place.
Return a non-null value to bypass WordPress' default site queries.
The expected return type from this filter depends on the value passed in the request query vars:
$this->query_vars['count']is set, the filter should return the site count as an integer.
'ids' === $this->query_vars['fields'], the filter should return an array of site IDs.
- Otherwise the filter should return an array of WP_Site objects.
Note that if the filter returns an array of site data, it will be assigned
sites property of the current WP_Site_Query instance.
Filtering functions that require pagination information are encouraged to set
max_num_pages properties of the WP_Site_Query object,
passed to the filter by reference. If WP_Site_Query does not perform a database
query, it will not have enough information to generate these values itself.