Write a test to check that ConnectionMode.polling is enabled

[IvoneDjaja]

Is your feature request related to a problem? Please describe.
I am trying to enable polling mode in LDClient and I want to test that the polling connection mode is enabled, but I can't because config is passed to private _connectionManager and not exposed.

Enable polling mode for the SDK when testing in BrowserStack. This is done by adjusting the configuration options when initializing the SDK.
From https://support.launchdarkly.com/hc/en-us/articles/17478871815963-How-to-configure-SDK-to-be-compatible-with-BrowserStack

# my_repository/lib/ld_client.dart
Future<LDClient> initLDClient({
  required String sdkKey,
}) async {
  final context = LDContextBuilder().build();
  final client = LDClient(
    LDConfig(
      sdkKey,
      AutoEnvAttributes.enabled,
      dataSourceConfig: DataSourceConfig(
        initialConnectionMode:
            ConnectionMode.polling,
      ),
    ),
    context,
  );
  return client;
}

Describe the solution you'd like

# launchdarkly_flutter_client_sdk-4.11.1/lib/src/ld_client.dart
interface class LDClient {
  // create a getter
 ConnectionMode get connectionMode => _connectionManager.config.initialConnectionMode;
}

# my_repository/test/ld_client_test.dart
test('Should set connection to polling', () async {
  final client = await initLDClient(
    sdkKey: 'test-sdk-key',
  );
  expect(client, isA<LDClient>());
  expect(client.connectionMode, ConnectionMode.polling);
});

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context about the feature request here.

[tanderson-ld]

Thank you for taking the time to document this feature request. I have logged it internally as 1275.