docs: document SLACK_MULTI_AGENT_CHANNEL_ENABLED for self-hosted (#546)

Author: tatianainama

self-host/customize-deployment/environment-variables.mdx

@@ -341,6 +341,7 @@ These variables enable you to configure the [Slack integration](/guides/using-sl
 | `SLACK_SOCKET_MODE`          | Enable socket mode for Slack (default=false)                              |
 | `SLACK_CHANNELS_CACHED_TIME` | Time in milliseconds to cache Slack channels (default=600000, 10 minutes) |
 | `SLACK_SUPPORT_URL`          | URL for Slack support                                                     |
+| `SLACK_MULTI_AGENT_CHANNEL_ENABLED` | Enables the [multi-agent Slack channel (Beta)](/guides/ai-agents/getting-started#setting-up-a-multi-agent-slack-channel) feature for the whole instance (default=false) |
 
 ## GitHub Integration
 

self-host/enterprise-on-prem.mdx

@@ -51,6 +51,7 @@ Once your license key is active, most Enterprise features are controlled by envi
 |---------|---------------------|---------------|
 | Custom roles | `CUSTOM_ROLES_ENABLED=true` | [Custom roles](/references/workspace/custom-roles#custom-roles) |
 | AI agents | `AI_AGENTS_ENABLED=true` | [AI agents](/guides/ai-agents) |
+| Multi-agent Slack channels (Beta) | `SLACK_MULTI_AGENT_CHANNEL_ENABLED=true` | [Multi-agent Slack channels](/guides/ai-agents/getting-started#setting-up-a-multi-agent-slack-channel) |
 | Caching | `RESULTS_CACHE_ENABLED=true` | [Caching](/guides/developer/caching) |
 | Embedding | `EMBEDDING_ENABLED=true` | [Embedding](/references/embedding) |
 | MCP | `MCP_ENABLED=true` | [MCP integration](/self-host/customize-deployment/configure-mcp-for-lightdash) |