[MCP] Add auth status to MCP servers (#4918)

This adds a queryable auth status for MCP servers which is useful:
1. To determine whether a streamable HTTP server supports auth or not
based on whether or not it supports RFC 8414-3.2
2. Allow us to build a better user experience on top of MCP status

codex-rs/rmcp-client/Cargo.toml

@@ -12,6 +12,7 @@ axum = { workspace = true, default-features = false, features = [
     "http1",
     "tokio",
 ] }
+codex-protocol = { workspace = true }
 keyring = { workspace = true, features = [
     "apple-native",
     "crypto-rust",