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/constants.ts

@@ -85,6 +85,7 @@ export const LICENSE_FEATURES = {
 	WORKFLOW_HISTORY: 'feat:workflowHistory',
 	DEBUG_IN_EDITOR: 'feat:debugInEditor',
 	BINARY_DATA_S3: 'feat:binaryDataS3',
+	MULTIPLE_MAIN_INSTANCES: 'feat:multipleMainInstances',
 } as const;
 
 export const LICENSE_QUOTAS = {