chore: Update sdk_metadata features (#221)

**Requirements**

- [x] I have added test coverage for new or changed functionality (N/A -
metadata only)
- [x] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [x] I have validated my changes against all supported platform
versions (N/A - metadata only)

**Related issues**

N/A

**Describe the solution you've provided**

Updates the `.sdk_metadata.json` file to include all features supported
by the LaunchDarkly.ServerSdk. Previously, only the `hooks` feature was
listed. This PR adds 21 features with their introduction versions,
organized in alphabetical order.

Features added:
- `allFlags` (2.0), `appMetadata` (8.0), `bigSegments` (6.2), `contexts`
(7.0), `experimentation` (6.1), `fdv2` (8.11), `fileDataSource` (5.5),
`flagChanges` (6.0), `inlineContextCustomEvents` (8.8), `migrations`
(8.0), `offlineMode` (1.0), `otel` (8.4), `privateAttrs` (3.5),
`relayProxyDaemon` (5.2), `relayProxyProxy` (1.0), `secureMode` (2.0),
`storingData` (1.0), `testDataSource` (6.0), `track` (1.0),
`variationDetail` (5.4), `webProxy` (1.0)

**Describe alternatives you've considered**

N/A

**Additional context**

- Feature keys sourced from
[feature_info.json](https://github.com/launchdarkly/sdk-meta/blob/main/products/feature_info.json)
- Feature versions sourced from the [SDK features
documentation](https://github.com/launchdarkly/ld-docs-private/blob/587f1518865abdf4ffc3bcb9cf08c3a67b2f8540/fern/topics/sdk/index.mdx)
(server-side SDKs A-K table, .NET column)
- Versions verified against
[CHANGELOG.md](https://github.com/launchdarkly/dotnet-core/blob/main/pkgs/sdk/server/CHANGELOG.md)

A detailed comment with source links for each feature version will be
added to this PR.

---
Link to Devin run:
https://app.devin.ai/sessions/874d797aa06e4051977b283dcd46cfd2
Requested by: rlamb@launchdarkly.com

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Metadata-only change; risk is limited to incorrect feature/version
mapping affecting downstream reporting or docs generation.
> 
> **Overview**
> Updates `.sdk_metadata.json` for the `.NET Server SDK` to enumerate
supported capabilities, expanding `features` from just `hooks` to a
full, alphabetized set of feature flags with their `introduced` versions
(e.g., `contexts`, `bigSegments`, `otel`, `fdv2`, `offlineMode`, etc.).
> 
> No runtime code changes; this is metadata-only and should primarily
affect tooling/reporting that consumes SDK feature capability data.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
490672d. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: rlamb@launchdarkly.com <rlamb@launchdarkly.com>

Author: devin-ai-integration[bot]

.sdk_metadata.json

@@ -9,8 +9,71 @@
         "C#"
       ],
       "features": {
+        "allFlags": {
+          "introduced": "2.0"
+        },
+        "appMetadata": {
+          "introduced": "8.0"
+        },
+        "bigSegments": {
+          "introduced": "6.2"
+        },
+        "contexts": {
+          "introduced": "7.0"
+        },
+        "experimentation": {
+          "introduced": "6.1"
+        },
+        "fdv2": {
+          "introduced": "8.11"
+        },
+        "fileDataSource": {
+          "introduced": "5.5"
+        },
+        "flagChanges": {
+          "introduced": "6.0"
+        },
         "hooks": {
           "introduced": "8.3"
+        },
+        "inlineContextCustomEvents": {
+          "introduced": "8.8"
+        },
+        "migrations": {
+          "introduced": "8.0"
+        },
+        "offlineMode": {
+          "introduced": "1.0"
+        },
+        "otel": {
+          "introduced": "8.4"
+        },
+        "privateAttrs": {
+          "introduced": "3.5"
+        },
+        "relayProxyDaemon": {
+          "introduced": "5.2"
+        },
+        "relayProxyProxy": {
+          "introduced": "1.0"
+        },
+        "secureMode": {
+          "introduced": "2.0"
+        },
+        "storingData": {
+          "introduced": "1.0"
+        },
+        "testDataSource": {
+          "introduced": "6.0"
+        },
+        "track": {
+          "introduced": "1.0"
+        },
+        "variationDetail": {
+          "introduced": "5.4"
+        },
+        "webProxy": {
+          "introduced": "3.2"
         }
       },
       "releases": {