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_

未指定任何文件、测试或入口点。首先定位 CLI 中的任务和会话请求处理，然后明确 token 限制和确认选项应如何工作。完成的标准是：对请求或会话实施了该限制，并且测试覆盖了提议的预算响应。

由索引模型根据 Issue 内容生成。