Add warning_budget_increment parameter to trigger warnings at cost thresholds

[xingyaoww]

This PR implements a mechanism that pauses the agent when the accumulated cost reaches certain thresholds and shows a toast notification in the frontend asking for user approval to continue.

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:32169bc-nikolaik   --name openhands-app-32169bc   docker.all-hands.dev/all-hands-ai/openhands:32169bc