Allow full configuration file for the Event Handler chart

[programmerq]

What would you like Teleport to do?

The event handler chart https://github.com/gravitational/teleport/tree/v17.3.3/examples/chart/event-handler should allow the users to set any arbitrary configuration option, including start_time.

What problem does this solve?

The chart currently goes with a completely unset start_time value. A user that wants to ingest older events can't do that with the chart as it is.

If a workaround exists, please include it.

The chart doesn't expose extraEnv to set variables, nor does it have any hooks for initContainers or toml overrides to merge into the rendered config file.