Declare experimental Amazon Bedrock setup APIs (#39277)

## What changed

- Add experimental `account/bedrock/discover` and `account/bedrock/setup`
  requests to the app-server protocol.
- Define discovery results for AWS profiles and environment credentials, plus
  setup inputs for profiles, environment credentials, and access keys.
- Export the new types in the experimental protocol schema. The app server
  currently returns `method not found` for both requests because setup is not
  yet implemented.

GitOrigin-RevId: 656b4bc11231a417e97041068cecc5dc692786e3

codex-rs/app-server/src/message_processor.rs

@@ -1501,6 +1501,9 @@ impl MessageProcessor {
                     .login_account(request_id.clone(), params)
                     .await
             }
+            ClientRequest::BedrockDiscover { .. } | ClientRequest::BedrockSetup { .. } => Err(
+                crate::error_code::method_not_found("Amazon Bedrock setup is not implemented"),
+            ),
             ClientRequest::LogoutAccount { .. } => {
                 self.account_processor
                     .logout_account(request_id.clone())