Create Dart snippets and reference them

Co-Authored-By: ok300 <106775972+ok300@users.noreply.github.com>

snippets/dart_snippets/lib/getting_started.dart

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+import 'dart:typed_data';
+
+import 'package:breez_sdk/breez_sdk.dart';
+import 'package:breez_sdk/bridge_generated.dart';
+
+Future<void> initializeSDK() async {
+  // ANCHOR: init-sdk
+
+  // Initialize SDK logs listener
+  BreezSDK().initialize();
+
+// Create the default config
+  Uint8List seed = await BreezSDK().mnemonicToSeed("<mnemonic words>");
+  String inviteCode = "<invite code>";
+  String apiKey = "<api key>";
+  NodeConfig nodeConfig = NodeConfig.greenlight(
+    config: GreenlightNodeConfig(
+      partnerCredentials: null,
+      inviteCode: inviteCode,
+    ),
+  );
+  Config config = await BreezSDK().defaultConfig(
+    envType: EnvironmentType.Production,
+    apiKey: apiKey,
+    nodeConfig: nodeConfig,
+  );
+
+  // Customize the config object according to your needs
+  config = config.copyWith(workingDir: "path to an existing directory");
+
+  // Connect to the Breez SDK make it ready for use
+  return await BreezSDK().connect(config: config, seed: seed);
+  // ANCHOR_END: init-sdk
+}
+
+Future<void> fetchBalance(String lspId) async {
+  // ANCHOR: fetch-balance
+  NodeState? nodeInfo = await BreezSDK().nodeInfo();
+  if (nodeInfo != null) {
+    int lnBalance = nodeInfo.channelsBalanceMsat;
+    int onchainBalance = nodeInfo.onchainBalanceMsat;
+    print(lnBalance);
+    print(onchainBalance);
+  }
+  // ANCHOR_END: fetch-balance
+}