Support bearerToken for BYO-K

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

In corp context, key based auth is disabled per compliance requirements. BearedToken based auth or customized broker would be helpful to automate the CLI runs.

### Proposed solution

Similar as what have been offered in GitHub Copilot SDK.
https://docs.github.com/en/copilot/how-tos/copilot-sdk/auth/byok#providerconfig-fields

field| type| description
-- | -- | --
bearerToken / bearer_token | string | Bearer token auth (takes precedence over apiKey)
bearerTokenProvider / bearer_token_provider | callback | Returns a bearer token on demand (takes precedence over apiKey and bearerToken)

### Example prompts or workflows

_No response_

### Additional context

_No response_

先阅读现有的 CLI BYO-K 配置和 apiKey 身份验证流程，然后将其与所链接的 GitHub Copilot SDK provider 字段进行比较。当 CLI 运行可以使用 bearerToken 或 bearerTokenProvider 进行身份验证，并且这些选项优先于 apiKey 时，即视为完成。

由索引模型根据 Issue 内容生成。