Implement BullMQ for background job processing

* new REDIS_URL environment variable

apps/server/src/integrations/mail/processors/email.processor..ts

@@ -0,0 +1,39 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { OnWorkerEvent, Processor, WorkerHost } from '@nestjs/bullmq';
+import { QueueName } from '../../queue/constants';
+import { Job } from 'bullmq';
+import { MailService } from '../mail.service';
+
+@Injectable()
+@Processor(QueueName.EMAIL_QUEUE)
+export class EmailProcessor extends WorkerHost {
+  private readonly logger = new Logger(EmailProcessor.name);
+  constructor(private readonly mailService: MailService) {
+    super();
+  }
+
+  async process(job: Job): Promise<void> {
+    try {
+      await this.mailService.sendEmail(job.data);
+    } catch (err) {
+      throw err;
+    }
+  }
+
+  @OnWorkerEvent('active')
+  onActive(job: Job) {
+    this.logger.debug(`Processing ${job.name} job`);
+  }
+
+  @OnWorkerEvent('failed')
+  onError(job: Job) {
+    this.logger.warn(
+      `Error processing ${job.name} job. Reason: ${job.failedReason}`,
+    );
+  }
+
+  @OnWorkerEvent('completed')
+  onCompleted(job: Job) {
+    this.logger.debug(`Completed ${job.name} job`);
+  }
+}