External type submission with metadata for 'related resources' can't be edited

[pkdash]

Description of the bug
If a resource is registered from External repository with metadata for 'Related Resources', the resource gets submitted and is listed in my submissions page. However, trying to load that resource for editing, generates error from the server.

Looking at the metadata stored for such a resource, it seems the 'type' field of the relation object gets set to the Type enum field name rather than the value of that enum field. That causes the error when loading the metadata.

Steps to reproduce the bug:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Additional information
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