Allow setting a channel for new users to auto-join (#9291)

Release Notes:

- Automatically add new users to the #zed channel

crates/collab/src/lib.rs

@@ -11,7 +11,7 @@ mod tests;
 use anyhow::anyhow;
 use aws_config::{BehaviorVersion, Region};
 use axum::{http::StatusCode, response::IntoResponse};
-use db::Database;
+use db::{ChannelId, Database};
 use executor::Executor;
 use serde::Deserialize;
 use std::{path::PathBuf, sync::Arc};
@@ -128,6 +128,7 @@ pub struct Config {
     pub zed_environment: Arc<str>,
     pub zed_client_checksum_seed: Option<String>,
     pub slack_panics_webhook: Option<String>,
+    pub auto_join_channel_id: Option<ChannelId>,
 }
 
 impl Config {