port ai crate to ai2, with all tests passing

crates/ai2/src/auth.rs

@@ -0,0 +1,17 @@
+use async_trait::async_trait;
+use gpui2::AppContext;
+
+#[derive(Clone, Debug)]
+pub enum ProviderCredential {
+    Credentials { api_key: String },
+    NoCredentials,
+    NotNeeded,
+}
+
+#[async_trait]
+pub trait CredentialProvider: Send + Sync {
+    fn has_credentials(&self) -> bool;
+    async fn retrieve_credentials(&self, cx: &mut AppContext) -> ProviderCredential;
+    async fn save_credentials(&self, cx: &mut AppContext, credential: ProviderCredential);
+    async fn delete_credentials(&self, cx: &mut AppContext);
+}