chore: migrating current react features (#1235)

This PR copies the react features that are in
https://github.com/launchdarkly/react-client-sdk/blob/main/.sdk_metadata.json
to the new `js-core` react sdk met.

NOTE: there will be another PR to add in features that are supported in
the new sdk (if any)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk metadata-only change, but incorrect feature/version mappings
could mislead tooling or documentation that consumes this file.
> 
> **Overview**
> Updates `.sdk_metadata.json` to replace the React SDK’s single
`contexts` feature entry with a full, versioned feature matrix (for
example `allFlags`, `bootstrapping`, `secureMode`, `hooks`, and others),
aligning React metadata with the upstream React client SDK feature list.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
1684feb. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

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Author: joker23

.sdk_metadata.json

@@ -178,7 +178,21 @@
       },
       "wrapperNames": ["react-client-sdk"],
       "features": {
-        "contexts": { "introduced": "0.0.1" }
+        "allFlags": { "introduced": "2.9" },
+        "appMetadata": { "introduced": "2.26" },
+        "bigSegments": { "introduced": "2.9" },
+        "bootstrapping": { "introduced": "2.9.5" },
+        "contexts": { "introduced": "3.0" },
+        "experimentation": { "introduced": "2.9" },
+        "flagChanges": { "introduced": "2.9" },
+        "hooks": { "introduced": "3.7" },
+        "perContextSummaryEvents": { "introduced": "3.8" },
+        "pluginSupport": { "introduced": "3.7" },
+        "privateAttrs": { "introduced": "2.9" },
+        "relayProxyProxy": { "introduced": "2.9" },
+        "secureMode": { "introduced": "2.18" },
+        "track": { "introduced": "2.9" },
+        "variationDetail": { "introduced": "2.21" }
       }
     },
     "server-ai": {