Add a way to comment on pull requests that were created with bunaider

[seveibar]

• Give an example of how it can be used in a github workflow
• If bunaider fix <pr number> is run (instead of an issue number, a PR number is provided) then scan the PR comments and add them into the aider message
• Do not modify the .github/workflows directory
• When responding to pull request comments, make sure that aider receives the original issue content in it's message as well as any comments prefixed with aider: on it's message.
• If a comment is made on a specific file, include the specific file path in the message next to the comment
• Only initialize the action when a pull request gets "Request Changes" on it with "aider: " in the comment