Discussion modules created in split courses have unstable discussion IDs

Description

If you add a Discussion module to a course backed by split mongo, the "Discussion ID" it displays will change every time you refresh the page - until you've made and saved an edit to the discussion module (such as setting its display_name).

This is inconsistent with old mongo and could be problematic for any integrations that depend on the Discussion ID.

Steps to Reproduce

1. Create a course while split is set as the default modulestore (Set `DEFAULT_STORE_FOR_NEW_COURSE` to `split`)
2. In the new course, create a Section, Subsection, and Unit
3. In the new Unit, add a Discussion block. Do not "Edit" the block.
4. Refresh the Unit page in studio and notice the Discussion ID changes every time.

Current Behavior

None

Expected Behavior

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Reason for Variance

None

Release Notes

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User Impact Summary

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Assignee

Unassigned

Reporter

Braden MacDonald

Labels

Reach

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Impact

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Platform Area

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Customer

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Partner Manager

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URL

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Contributor Name

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Groups with Read-Only Access

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Actual Points

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Category of Work

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Platform Map Area (Levels 1 & 2)

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Platform Map Area (Levels 3 & 4)

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Priority

CAT-3
Configure