feat(core): Set up leader selection for multiple main instances (#7527)

https://linear.app/n8n/issue/PAY-933/set-up-leader-selection-for-multiple-main-instances

- [x] Set up new envs
- [x] Add config and license checks
- [x] Implement `MultiMainInstancePublisher`
- [x] Expand `RedisServicePubSubPublisher` to support
`MultiMainInstancePublisher`
- [x] Init `MultiMainInstancePublisher` on startup and destroy on
shutdown
- [x] Add to sandbox plans
- [x] Test manually

Note: This is only for setup - coordinating in reaction to leadership
changes will come in later PRs.

packages/cli/src/ExternalSecrets/ExternalSecretsManager.ee.ts

@@ -19,7 +19,7 @@ import {
 import { License } from '@/License';
 import { InternalHooks } from '@/InternalHooks';
 import { ExternalSecretsProviders } from './ExternalSecretsProviders.ee';
-import { OrchestrationMainService } from '@/services/orchestration/main/orchestration.main.service';
+import { SingleMainInstancePublisher } from '@/services/orchestration/main/SingleMainInstance.publisher';
 
 @Service()
 export class ExternalSecretsManager {
@@ -82,7 +82,7 @@ export class ExternalSecretsManager {
 	}
 
 	async broadcastReloadExternalSecretsProviders() {
-		await Container.get(OrchestrationMainService).broadcastReloadExternalSecretsProviders();
+		await Container.get(SingleMainInstancePublisher).broadcastReloadExternalSecretsProviders();
 	}
 
 	private decryptSecretsSettings(value: string): ExternalSecretsSettings {