[Resolver] Add warnings for migration

[neubig]

We are performing a refactor by moving openhands-resolver to Openhands (see details).

There are still users that are using openhands-resolver that may not be aware of this refactor. It would be beneficial to include the following changes

1. Warnings statements when openhands-resolver program starts running, with a link to instructions for setting up the latest refactored version
2. People may be using openhands-resolver through Github actions primarily, thus missing the warning statement in step 1. It would be helpful to include an additional blurb when creating PRs using openhands-resolver. Alternatively, the blurb could be included in the Git Bot messages.

Example blurb

ALERT: message from your friendly neighborhood code agent -> we're migrating .....

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Moved from All-Hands-AI/openhands-resolver#345

[neubig]

This should be solved in the resolver repo