feat: Add Resend node and trigger

Adds a new integration for Resend, an email sending service.

Includes:
- Resend API credential (`ResendApi.credentials.ts`) for API key authentication.
- Resend action node (`nodes/Resend/Resend.node.ts`):
  - Supports "Send Email" operation with parameters for to, from, subject, html, text, cc, bcc, reply_to, and tags.
  - Uses Resend API `https://api.resend.com/emails`.
- Resend trigger node (`nodes/Resend/ResendTrigger.node.ts`):
  - Handles Resend webhooks for various event types (email.sent, email.delivered, etc.).
  - Implements webhook signature verification using Svix and a user-provided signing secret.
  - Allows you to select which events to listen for.
- Official Resend SVG icon (`nodes/Resend/Resend.svg`).
- Adds `svix` as a dependency for webhook verification.

credentials/ResendApi.credentials.ts

@@ -0,0 +1,27 @@
+import {
+	ICredentialType,
+	INodeProperties,
+	IAuthData,
+} from 'n8n-workflow';
+
+export class ResendApi implements ICredentialType {
+	name = 'resendApi';
+	displayName = 'Resend API';
+	documentationUrl = 'https://resend.com/docs/api-reference/introduction';
+	properties: INodeProperties[] = [
+		{
+			displayName: 'API Key',
+			name: 'apiKey',
+			type: 'string',
+			default: '',
+			required: true,
+		},
+	];
+	// Use IAuthData for authentication
+	authenticate: IAuthData = {
+		type: 'apiToken',
+		properties: {
+			token: '={{$credentials.apiKey}}'
+		}
+	};
+}