Add Missing config in workflow threshold page

The page lists the 'bug_reminder_threshold' (i.e. access level needed
for users to send reminders) configuration, but does not allow the admin
to set its counterpart 'reminder_receive_threshold'.

Fixes #15360

lang/strings_english.txt

@@ -1370,6 +1370,7 @@ If you requested this verification, visit the following URL to change your passw
 	'others' => 'Others',
 	'see_email_addresses_of_other_users' => 'See e-mail addresses of other users',
 	'send_reminders' => 'Send reminders',
+	'receive_reminders' => 'Receive reminders',
 	'add_profiles' => 'Add profiles',
 	'notify_of_new_user_created' => 'Notify of new user created',
 	'email_notification' => 'E-mail notification',

manage_config_work_threshold_page.php

@@ -338,6 +338,7 @@ function get_section_end() {
 get_capability_row( lang_get( 'view' ) . ' ' . lang_get( 'assigned_to' ), 'view_handler_threshold' );
 get_capability_row( lang_get( 'view' ) . ' ' . lang_get( 'bug_history' ), 'view_history_threshold' );
 get_capability_row( lang_get( 'send_reminders' ), 'bug_reminder_threshold' );
+get_capability_row( lang_get( 'receive_reminders' ), 'reminder_receive_threshold' );
 get_section_end();