Add support for getting members of a GitHub team

[DylanBettermannDD]

Describe the feature or problem you’d like to solve

In CODEOWNERS we leverage GitHub teams as much as possible to avoid further code changes when teams change. I want to be able to ask the AI agent "who owns X code?", which finds the CODEOWNERS entry, and then uses the GitHub MCP server to produce the list of team members.

Proposed solution

Add GitHub team support to the MCP implementation.

Additional context

None right now, but will add if I think of any.