[Feat]: Adding macro invocation for Github issues

[malhotra5]

This PR partially address issue #232

Changes

1. You can now trigger Openhands for Github issues by leaving a new comment on the issue with the macro @openhands-agent
2. Openhands only considers the new comment with macro, and the original title/body of the issue as context
3. If you want Openhands to use every comment on an issue as context, the fix-me label should be used instead of the macro

Sample test with macro

Workflow log

Future work

I'm thinking of doing the following work on separate PRs

1. Starting the resolver from comments containing macro on PRs
2. Allowing users to customize the macro that triggers the resolver

[neubig]

Looks great, thanks! I think this fixes https://github.com/All-Hands-AI/openhands-resolver/issues/232

[malhotra5]

I think it only partially fixes #232; need to add similar functionality for PR comments as well 🙂