mod_groups_internal: allow force-emitting group member addition events This is useful when a new plugin was loaded which handles that event to add some value. Then the command can be called (**not** from the plugin but from an upcoming admin shell module) to synchronise things.

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summary: Log a message once per minute
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This module sends `-- MARK --` to the log once per minute. This may be
useful to give a sense of how busy the server is or see that logging and
timers are still working.