feat: Add get organization members and list all outside collaborators of an organization

[cointem]

This pull request adds two new tools for organization management in the GitHub integration, along with their documentation, implementation, and test coverage. The new tools enable fetching organization members and listing outside collaborators, both with support for pagination and filtering. The changes are grouped into tool additions, documentation updates, and test enhancements.

New organization management tools:

• Added the get_org_members tool, which retrieves members of a specified organization, with support for pagination and filtering by role (all, admin, member). [1] [2]
• Added the list_outside_collaborators tool, which lists users who have access to organization repositories but are not organization members, also supporting pagination. [1] [2]
• Registered both new tools in the default toolset group so they are available for use.

Documentation updates:

• Updated README.md to include usage details for the new get_org_members and list_outside_collaborators tools, including their parameters and descriptions.

Test coverage:

• Added comprehensive unit tests for both new tools, covering successful calls, empty results, client errors, and API errors.

These changes improve the ability to manage and audit organization membership and access via the GitHub integration.

[cointem]

refs #1331