Migrate PR reviewer from software-agent-sdk repo

[juanmichelini]

Sibling issue to OpenHands/software-agent-sdk#2282

We are currently maintaining two versions of the PR review bot, and we want to maintain only one.

We want to close the implementation gap of the software-agent-sdk with the extensions repo.
See

• https://github.com/OpenHands/software-agent-sdk/blob/main/.github/actions/pr-review/action.yml and
• https://docs.openhands.dev/openhands/usage/use-cases/code-review#repository-specific-review-guidelines