Add assignee_id parameter to search_issues tool

[codegen-sh]

Overview

This PR adds an optional assignee_id parameter to the search_issues tool, allowing users to filter GitHub issues and PRs by assignee directly through a parameter instead of having to manually include it in the search query string.

Changes

• Added an optional assignee_id parameter to the GithubSearchIssuesInput class
• Updated the GithubSearchIssuesTool._run method to handle the new parameter by appending assignee:{assignee_id} to the query if provided
• Updated the tool description to mention the new parameter
• Updated the docstring in the search function to document the new parameter

Testing

The implementation ensures backward compatibility with existing code that doesn't use this parameter. When the assignee_id parameter is provided, it automatically adds the appropriate filter to the search query.

Related Issue

Resolves: Add assignee_id parameter to search_issues tool