feat(core): Coordinate manual workflow activation and deactivation in multi-main scenario (#7643)

Followup to #7566 | Story: https://linear.app/n8n/issue/PAY-926

### Manual workflow activation and deactivation

In a multi-main scenario, if the user manually activates or deactivates
a workflow, the process (whether leader or follower) that handles the
PATCH request and updates its internal state should send a message into
the command channel, so that all other main processes update their
internal state accordingly:

- Add to `ActiveWorkflows` if activating
- Remove from `ActiveWorkflows` if deactivating
- Remove and re-add to `ActiveWorkflows` if the update did not change
activation status.

After updating their internal state, if activating or deactivating, the
recipient main processes should push a message to all connected
frontends so that these can update their stores and so reflect the value
in the UI.

### Workflow activation errors

On failure to activate a workflow, the main instance should record the
error in Redis - main instances should always pull activation errors
from Redis in a multi-main scenario.

### Leadership change

On leadership change...

- The old leader should stop pruning and the new leader should start
pruning.
- The old leader should remove trigger- and poller-based workflows and
the new leader should add them.

packages/cli/src/config/schema.ts

@@ -1324,24 +1324,29 @@ export const schema = {
 		},
 	},
 
-	leaderSelection: {
+	multiMainSetup: {
+		instanceType: {
+			doc: 'Type of instance in multi-main setup',
+			format: ['unset', 'leader', 'follower'] as const,
+			default: 'unset', // only until first leader key check
+		},
 		enabled: {
-			doc: 'Whether to enable leader selection for multiple main instances (license required)',
+			doc: 'Whether to enable multi-main setup for queue mode (license required)',
 			format: Boolean,
 			default: false,
-			env: 'N8N_LEADER_SELECTION_ENABLED',
+			env: 'N8N_MULTI_MAIN_SETUP_ENABLED',
 		},
 		ttl: {
-			doc: 'Time to live in Redis for leader selection key, in seconds',
+			doc: 'Time to live (in seconds) for leader key in multi-main setup',
 			format: Number,
 			default: 10,
-			env: 'N8N_LEADER_SELECTION_KEY_TTL',
+			env: 'N8N_MULTI_MAIN_SETUP_KEY_TTL',
 		},
 		interval: {
-			doc: 'Interval in Redis for leader selection check, in seconds',
+			doc: 'Interval (in seconds) for leader check in multi-main setup',
 			format: Number,
 			default: 3,
-			env: 'N8N_LEADER_SELECTION_CHECK_INTERVAL',
+			env: 'N8N_MULTI_MAIN_SETUP_CHECK_INTERVAL',
 		},
 	},