enhancement: add tool to request reviewers for pull requests

[MayorFaj]

This pull request introduces a new feature to request reviewers for a pull request in the GitHub MCP tool. The changes include updates to the documentation, implementation of the new tool, and corresponding tests. Below are the most important changes:

New Feature Implementation:

• pkg/github/pullrequests.go: Added the RequestPullRequestReviewers function to create a tool for requesting reviewers for a pull request. This includes defining the tool's input schema, extracting parameters, and making the API call to GitHub.

Documentation Updates:

• README.md: Updated to include documentation for the new request_pull_request_reviewers tool, detailing its parameters and usage. [1] [2]

Test Cases:

• pkg/github/pullrequests_test.go: Added tests for the new RequestPullRequestReviewers function to verify the tool definition and various scenarios, including successful requests and error handling.

Server Integration:

• pkg/github/server.go: Integrated the new RequestPullRequestReviewers tool into the server setup, ensuring it is available for use.

Closes: #259

[Copilot]

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

[juruen]

@MayorFaj thank you again for your time working on this project!

I have a suggestion, instead of creating a new tool, we could leverage the existing update_pull_request tool to also take the reviewers as an optional parameter.

Is that something that you'd like to explore? Otherwise, I can take a stab at it when I have the time.

Thanks!

[MayorFaj]

Sure will take a look

[MayorFaj]

@juruen I made a new PR #285. Kindly review when you get the chance to. I am going to close this

[tonytrg]

follow up pr #285