chore(server): support disable indexer plugin (#12408)

close CLOUD-220

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **New Features**
  - Introduced a new service to handle indexing-related events and scheduled tasks, improving the management of document and workspace indexing.
  - Added support for configuring the indexer feature via the AFFINE_INDEXER_ENABLED environment variable.

- **Bug Fixes**
  - Ensured that indexing and deletion jobs are only enqueued when the indexer feature is enabled.

- **Tests**
  - Added comprehensive tests for the new indexing event service, covering various configuration scenarios.
  - Removed obsolete test related to auto-indexing scheduling.

- **Chores**
  - Updated configuration descriptions and mappings to improve clarity and environment variable support.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/indexer/event.ts

@@ -0,0 +1,86 @@
+import { Injectable } from '@nestjs/common';
+import { Cron, CronExpression } from '@nestjs/schedule';
+
+import { Config, JobQueue, OnEvent } from '../../base';
+
+@Injectable()
+export class IndexerEvent {
+  constructor(
+    private readonly queue: JobQueue,
+    private readonly config: Config
+  ) {}
+
+  @OnEvent('doc.updated')
+  async indexDoc({ workspaceId, docId }: Events['doc.updated']) {
+    if (!this.config.indexer.enabled) {
+      return;
+    }
+
+    await this.queue.add(
+      'indexer.indexDoc',
+      {
+        workspaceId,
+        docId,
+      },
+      {
+        jobId: `indexDoc/${workspaceId}/${docId}`,
+        priority: 100,
+      }
+    );
+  }
+
+  @OnEvent('workspace.updated')
+  async indexWorkspace({ id }: Events['workspace.updated']) {
+    if (!this.config.indexer.enabled) {
+      return;
+    }
+
+    await this.queue.add(
+      'indexer.indexWorkspace',
+      {
+        workspaceId: id,
+      },
+      {
+        jobId: `indexWorkspace/${id}`,
+        priority: 100,
+      }
+    );
+  }
+
+  @OnEvent('user.deleted')
+  async deleteUserWorkspaces(payload: Events['user.deleted']) {
+    if (!this.config.indexer.enabled) {
+      return;
+    }
+
+    for (const workspace of payload.ownedWorkspaces) {
+      await this.queue.add(
+        'indexer.deleteWorkspace',
+        {
+          workspaceId: workspace,
+        },
+        {
+          jobId: `deleteWorkspace/${workspace}`,
+          priority: 0,
+        }
+      );
+    }
+  }
+
+  @Cron(CronExpression.EVERY_30_SECONDS)
+  async autoIndexWorkspaces() {
+    if (!this.config.indexer.enabled) {
+      return;
+    }
+
+    await this.queue.add(
+      'indexer.autoIndexWorkspaces',
+      {},
+      {
+        // make sure only one job is running at a time
+        delay: 30 * 1000,
+        jobId: 'autoIndexWorkspaces',
+      }
+    );
+  }
+}