[docs] EAS workflows app_store_connect interpolation context docs (expo#44640)

# Why

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Please describe the motivation for this PR, and link to relevant GitHub
issues, forums posts, or feature requests.
-->

We've extended the workflows interpolation context with
`app_store_connect`.

# How

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How did you build this feature or fix this bug and why?
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Added the `app_store_connect` section to the EAS workflows syntax
documentation.

# Test Plan

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reproduce your test, especially if this PR does not include automated
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Tested manually:

<img width="625" height="794" alt="image"
src="https://github.com/user-attachments/assets/73183f5a-44fb-4a55-b988-57fa67ec2507"
/>

# Checklist

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Please check the appropriate items below if they apply to your diff.
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- [ ] I added a `changelog.md` entry and rebuilt the package sources
according to [this short
guide](https://github.com/expo/expo/blob/main/CONTRIBUTING.md#-before-submitting)
- [ ] This diff will work correctly for `npx expo prebuild` & EAS Build
(eg: updated a module plugin).
- [x] Conforms with the [Documentation Writing Style
Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)

---------

Co-authored-by: Stanisław Chmiela <sjchmiela@users.noreply.github.com>

Author: sswrk

docs/pages/eas/workflows/syntax.mdx

@@ -792,6 +792,44 @@ jobs:
         View details: ${{ workflow.url }}
 ```
 
+#### `app_store_connect`
+
+Information about App Store Connect entities associated with the workflow run. This context is available only for workflows triggered by an App Store Connect event. See [`on.app_store_connect`](#onapp_store_connect).
+
+```ts
+type AppStoreConnectContext = {
+  app: {
+    id: string;
+  };
+  build_upload?: {
+    id: string;
+    state: 'awaiting_upload' | 'processing' | 'failed' | 'complete';
+  };
+};
+```
+
+The `app_store_connect.build_upload` object is present only when the workflow is triggered by a `build_upload` event domain.
+
+Example:
+
+```yaml
+on:
+  app_store_connect:
+    build_upload:
+      states:
+        - complete
+
+jobs:
+  notify:
+    type: slack
+    params:
+      webhook_url: ${{ env.SLACK_WEBHOOK_URL }}
+      message: |
+        Upload complete for App Store Connect app: ${{ app_store_connect.app.id }}
+        Upload ID: ${{ app_store_connect.build_upload.id }}
+        Upload state: ${{ app_store_connect.build_upload.state }}
+```
+
 #### `env`
 
 A record of environment variables available in the current job context.