Use purposeful api from rmcp to override default client name

Since the release of RMCP 0.8.0, they have added a way to change the client name used for oauth.
https://github.com/modelcontextprotocol/rust-sdk/pull/469/files

Currently, this was achieved using a somewhat convoluted hack:
https://github.com/aws/amazon-q-developer-cli/blob/1fa1d74976e119459e99d50ccc40c87195de5547/crates/chat-cli/src/mcp_client/oauth_util.rs#L566-L621

We can get rid of this hack and just use the api as provided by the RMCP crate.

Inizia in crates/chat-cli/src/mcp_client/oauth_util.rs, intorno alle righe 566–621, e confronta l’API RMCP 0.8.0 descritta nella PR 469. Sostituisci l’override contorto del nome del client con l’API fornita, quindi verifica che il client OAuth utilizzi ancora il nome previsto.

Scritto dal modello di indicizzazione a partire dal testo della issue.