`ModelInstanceDocument doc.replace`, there are some fields that are not updated in db table

**Describe the bug**
``` javascript
const doc = await ModelInstanceDocument.create(ceramic, CONTENT0, midMetadata)
await doc.replace(CONTENT1)
```
but in postgress ,the db table only updates 2 fields(last_anchored_at&updated_at) when doc updated, CONTENT1 data is not updated to table,maybe other fields should be updated as well

https://github.com/ceramicnetwork/js-ceramic/blame/33e3c0969c0161d5dc17b55501775385241066be/packages/core/src/indexing/postgres/postgres-index-api.ts#L57

**Screenshots**
If applicable, add screenshots to help explain your problem.

Start in packages/core/src/indexing/postgres/postgres-index-api.ts around line 57 and reproduce the ModelInstanceDocument.create and doc.replace sequence shown in the issue. Compare the database row before and after replacement to determine which document fields remain unchanged; done means the expected CONTENT1 data and relevant updated fields are persisted in PostgreSQL.

Written by the indexing model from the issue text.