realm-react-model-merge: (DOCSP-26995) Reframe RN SDK open and close realm page (#2529)

## Pull Request Info

The Open and Close a Realm page needed a nearly complete overhaul
because these concepts are very different with `@realm/react`.

I plan to re-evaluate the "Key Concept" section after we've finished the
current Realm React epic.

### Jira

- https://jira.mongodb.org/browse/DOCSP-26995

### Staged Changes

- [Configure a
Realm](https://docs-mongodbcom-staging.corp.mongodb.com/realm/docsworker-xlarge/DOCSP-26995/sdk/react-native/realm-database/configure-a-realm/)

### Reminder Checklist

If your PR modifies the docs, you might need to also update some
corresponding
pages. Check if completed or N/A.

- [x] Create Jira ticket for corresponding docs-app-services update(s),
if any
- [x] Checked/updated Admin API
- [x] Checked/updated CLI reference

### Review Guidelines


[REVIEWING.md](https://github.com/mongodb/docs-realm/blob/master/REVIEWING.md)

### Animal wearing a hat


![](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTC2T1wlVitCxsZHwKb18NazHbiFmtF0_FeNw&usqp=CAU)

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Co-authored-by: Ben Perlmutter <[email protected]>