Add REST APIs for getting and adding contributors

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/collab/src/db/tests/contributor_tests.rs

@@ -0,0 +1,37 @@
+use super::Database;
+use crate::{db::NewUserParams, test_both_dbs};
+use std::sync::Arc;
+
+test_both_dbs!(
+    test_contributors,
+    test_contributors_postgres,
+    test_contributors_sqlite
+);
+
+async fn test_contributors(db: &Arc<Database>) {
+    db.create_user(
+        &format!("user1@example.com"),
+        false,
+        NewUserParams {
+            github_login: format!("user1"),
+            github_user_id: 1,
+        },
+    )
+    .await
+    .unwrap()
+    .user_id;
+
+    assert_eq!(db.get_contributors().await.unwrap(), Vec::<String>::new());
+
+    db.add_contributor("user1", 1, None).await.unwrap();
+    assert_eq!(
+        db.get_contributors().await.unwrap(),
+        vec!["user1".to_string()]
+    );
+
+    db.add_contributor("user2", 2, None).await.unwrap();
+    assert_eq!(
+        db.get_contributors().await.unwrap(),
+        vec!["user1".to_string(), "user2".to_string()]
+    );
+}