Create schedule plugin type and trigger

[pauldix]

The schedule plugin should get the same plugin API yielded to it that the wal plugins get. It should get one of these: https://github.com/influxdata/influxdb/blob/main/influxdb3_py_api/src/system_py.rs#L27-L31

The Python code should require a single function as the entry point named process_scheduled_call. It should look something like:

def process_scheduled_call(influxdb3_local, schedule_time, args=None):

The trigger definition should take a trigger_spec that is a schedule string like those used with cron. When the trigger is enabled, it should run in a background task and trigger off that schedule, or be able to be disabled.

An API and CLI should be added to support this new type.

An endpoint should be added to test these plugins, like the wal type. When the test runs it would run once and return the results to the caller. The CLI should be updated so that test can call for this type.