Also show the "Share" step when editing an existing event definition

## What?

When editing an existing event definition the "Share" step (introduced via #22411 for new event definitions only) should be displayed.

## Why?

* It's useful to see all aspects of the event definition's configuration when editing (e.g. confirm the share permissions are still appropriate).
* Customizing a newly cloned/duplicated event definition may require adjusting share permissions.
* It's slightly jarring not having a consistent experience when managing event definitions.

## Your Environment

* Graylog Version: `6.3.5` and `7.0.0`