chore: Update sdk_metadata features

[devin-ai-integration]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Note: This is a metadata-only change that doesn't require test coverage or platform validation.

Related issues

N/A

Describe the solution you've provided

This PR adds a features section to .sdk_metadata.json that documents all SDK features and the versions in which they were introduced. The feature list was compiled by:

1. Cross-referencing the SDK features documentation (PHP column in server-side SDKs L-Z table)
2. Using canonical feature keys from feature_info.json
3. Verifying versions against CHANGELOG.md

Features included (20 total):

• allFlags, appMetadata, bigSegments, contexts, experimentation, fileDataSource, inlineContextCustomEvents, migrations, offlineMode, privateAttrs, relayProxyDaemon, relayProxyProxy, secureMode, storingData, storingDataConsul, storingDataDynamodb, storingDataRedis, testDataSource, track, variationDetail

Describe alternatives you've considered

N/A

Additional context

Requested by @keelerm84

Human review checklist

• Verify version numbers are accurate against documentation and CHANGELOG
• Confirm no supported features are missing from the list
• Validate feature keys match canonical names in feature_info.json

Link to Devin run: https://app.devin.ai/sessions/c182c15478ec4922bf043b4e7addebd5

[devin-ai-integration]

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