Get PR timeline details

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

I would like to be able to get details about the timeline of the Pull Request.

### Proposed solution

Add the timeline events to the response of the pull_request_read MCP tool.

This will allow other agents to monitor for completion of the code changes done by Copilot agent, and based on that initiate some testing GH actions workflows.

### Example prompts or workflows (for tools/toolsets only)

My use case:
- I have many terraform modules for infrastructure provisioning. They often require azurerm/google providers updates. I am building an agent that decides when to create an issue in Github, assigns the Copilot to resolve and then it should run e2e infrastructure (provisioning,test,deletion) testing. But currently I cannot poll for the timeline event on the PR such as:

**Copilot finished work on behalf of [myuser](https://github.com/myuser) [16 hours ago](https://github.com/myorg/terraform-azurerm-storageaccount/pull/40#event-20558334944)**

If this timeline event is available in pull_request_read , then I can poll for it and agent would decide when to run the tests.