Add service tier id to config

Use service_tier_id strings in config TOML/profile handling and config edits while keeping legacy service_tier enum values mapped into request ids.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/thread-manager-sample/src/main.rs

@@ -161,6 +161,7 @@ fn new_config(model: Option<String>, arg0_paths: Arg0DispatchPaths) -> anyhow::R
         startup_warnings: Vec::new(),
         model,
         service_tier: None,
+        service_tier_id: None,
         review_model: None,
         model_context_window: None,
         model_auto_compact_token_limit: None,