fix: add required parameter to produce_event command

[rgraber]

When we upgraded openedx_events to the version where event_metadata was required, we forgot to update the produce_event command, which is only used for testing. This just creates and EventsMetadata object from the event type and passes it.

Merge checklist:
Check off if complete or not applicable:

• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Commits are squashed
• Noted any: Concerns, dependencies, deadlines, tickets, testing instructions