[Feat]: Implement A2A Authentication Handling in A2A Inspector

### Is your feature request related to a problem? Please describe.

Regarding the settings for Security and Security Schemes in the Agent Card:

Even if Security Schemes are configured in the Agent Card, the A2A Inspector does not use these settings to perform authentication. The A2A Inspector only verifies the format of the Agent Card and the returned JSON-RPC, so A2A authentication cannot proceed within the A2A Inspector.

After checking the timing of Security Schemes usage, it appears that the A2A Client retrieves the authentication link and token link from the Security Schemes when obtaining a token. Specifically, the A2A Inspector does not implement this part of the logic in the A2A Client regarding authentication.

### Describe the solution you'd like

Therefore, we would like to request the implementation of A2A authentication processing within the A2A Inspector. Specifically, the Inspector should be able to utilize the Security Schemes defined in the Agent Card to perform the authentication flow, including retrieving the authentication link and token link, and obtaining a token as per the A2A Client’s logic.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

A2A Inspector は現在、Agent Card 形式と JSON-RPC レスポンスを検証しますが、認証ロジックがありません。Security Schemes から認証リンクとトークンリンクを取得する A2A Client の実装を調査してください。作業には、これらの schemes を使用し、認証フローを実行してトークンを取得するよう inspector を変更することが含まれます。まず Agent Card のパースと Security Schemes の処理を行うコードを見つけ、その後、トークン取得ロジックを統合してください。

索引モデルが issue の本文から書いたものです。