Skip Account Processing Based on User Role in CLI Command

[ajvillegas]

This change introduces a CLI command flag for limiting the account processing to the listed user roles.

This is not an ideal solution, but one I had to implement as a quick fix for a project with millions of user accounts. Currently the get_users() call is ignoring the role__in or role__not_in parameters of the WP_User_Query when added, so this change looks up the user role and skips the processing if it doesn't match with the one provided when running the command.

[kadamwhite]

Should/could we be doing any periodic in-memory cleanup? e.g. this is VIP's guidance on managing in-memory cache resources in long-running commands, a process which used to use the (inappropriate) name stop_the_insanity(). (Glad they changed that function name!)

[rmccue]

There's a newer public API to do this, fyi: https://developer.wordpress.org/reference/functions/wp_cache_flush_runtime/