`/github` feature: search GitHub issues from a repository

[josefaidt]

Description

Add support for searching issues from a GitHub repository. Unfortunately adding this support may exceed the supported command depth by Discord, which would motivate the need for a separate /issues or /search command

Todo

• add command support for searching GitHub issues
• decide whether it is justified to create a new command
  • deprecate this issue in favor of tracking new issue if so, copy intent
• requirement: results should be displayed in an embed
• requirement: only show subset of results (e.g. first 5)
• optional: add buttons to allow callers to select an issue and retrieve the URL
• optional: privately respond with issue list
• optional: paginating results with buttons