Add runtime size configuration feature

[neubig]

This PR adds a new feature to configure the runtime size in the settings modal. Users can now choose between 1x (2 core, 8G) and 2x (4 core, 16G) options.

Changes include:

• Added a new REMOTE_RUNTIME_RESOURCE_FACTOR field to the Settings type
• Created a new RuntimeSizeSelector component
• Updated the SettingsForm component to include the new selector
• Modified getSettings and saveSettings functions to handle the new setting
• Updated tests to include the new setting
• Added documentation about the new runtime size option in the README.md file

Please review and let me know if any changes are needed.

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Notes:

1. Fixes [Feature Request]: Set RemoteRuntime size in frontend #5797
2. This is pending review by @neubig

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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:1bb6cb3-nikolaik   --name openhands-app-1bb6cb3   docker.all-hands.dev/all-hands-ai/openhands:1bb6cb3