Add data source documentation for google_firebase_android_app_config (#8457) (#5954)

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/8457.txt

@@ -0,0 +1,3 @@
+```release-note:none
+Documentation change only
+```

website/docs/d/firebase_android_app_config.html.markdown

@@ -0,0 +1,41 @@
+---
+subcategory: "Firebase"
+description: |-
+  A Google Cloud Firebase Android application configuration
+---
+
+# google\_firebase\_android\_app\_config
+
+A Google Cloud Firebase Android application configuration
+
+~> **Warning:** This resource is in beta, and should be used with the terraform-provider-google-beta provider.
+See [Provider Versions](https://terraform.io/docs/providers/google/guides/provider_versions.html) for more details on beta resources.
+
+To get more information about androidApp, see:
+
+* [API documentation](https://firebase.google.com/docs/projects/api/reference/rest/v1beta1/projects.androidApps)
+* How-to Guides
+    * [Official Documentation](https://firebase.google.com/)
+
+
+## Argument Reference
+The following arguments are supported:
+
+* `app_id` - (Required) The id of the Firebase Android App.
+
+- - -
+
+* `project` - (Optional) The ID of the project in which the resource belongs. If it
+    is not provided, the provider project is used.
+
+## Attributes Reference
+
+In addition to the arguments listed above, the following attributes are exported:
+
+* `config_filename` -
+  The filename that the configuration artifact for the AndroidApp is typically saved as.
+  For example: google-services.json
+
+* `config_file_contents` -
+  The contents of the JSON configuration file.
+  A base64-encoded string.