add messagebird API

improve code readability

fixed a minor error

packages/nodes-base/credentials/MessageBirdApi.credentials.ts

@@ -0,0 +1,14 @@
+import { ICredentialType, NodePropertyTypes } from 'n8n-workflow';
+
+export class MessageBirdApi implements ICredentialType {
+	name = 'messageBirdApi';
+	displayName = 'MessageBird API';
+	properties = [
+		{
+			displayName: 'API Key',
+			name: 'accessKey',
+			type: 'string' as NodePropertyTypes,
+			default: ''
+		}
+	];
+}