collab: Backfill github_user_created_at on users (#16600)

This PR adds a backfiller to backfill the `github_user_created_at`
column on users.

Release Notes:

- N/A

crates/collab/src/lib.rs

@@ -9,6 +9,7 @@ pub mod migrations;
 mod rate_limiter;
 pub mod rpc;
 pub mod seed;
+pub mod user_backfiller;
 
 #[cfg(test)]
 mod tests;
@@ -177,6 +178,7 @@ pub struct Config {
     pub stripe_api_key: Option<String>,
     pub stripe_price_id: Option<Arc<str>>,
     pub supermaven_admin_api_key: Option<Arc<str>>,
+    pub user_backfiller_github_access_token: Option<Arc<str>>,
 }
 
 impl Config {
@@ -235,6 +237,7 @@ impl Config {
             supermaven_admin_api_key: None,
             qwen2_7b_api_key: None,
             qwen2_7b_api_url: None,
+            user_backfiller_github_access_token: None,
         }
     }
 }