Allow to set a token limit for a task

### Describe the feature or problem you'd like to solve

Currently each request consumes a certain predicable amount of premium requests - this will change soon and make it completely unpredictable, a task might accidently eat up thwo whole budget for a month.

### Proposed solution

With the upcoming https://github.blog/news-insights/company-news/github-copilot-is-moving-to-usage-based-billing/ it becomes completely unpredictable how much costs a request possibly consumes.

It would therefore be good to set a limit per session / request. If the limit is approached, copilot should ask for confirmation what to do that could be:

1. Complete as soon as possible with what was already accomplished
2. Continue with an increased budget
3. ....

### Example prompts or workflows

_No response_

### Additional context

_No response_

ファイル、テスト、エントリーポイントは指定されていません。まず CLI でのタスクおよびセッションのリクエスト処理を見つけ、次にトークン制限と確認の選択肢がどのように機能すべきかを明確にします。リクエストまたはセッションに対して制限が適用され、提案された予算レスポンスがテストでカバーされていれば完了です。

索引モデルが issue の本文から書いたものです。