Enable the multi conversation UI for all users

[tofarr]

Enable the multi conversation UI for all users

• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below

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Remove the feature flag

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Link of any specific issues this addresses

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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:716823f-nikolaik   --name openhands-app-716823f   docker.all-hands.dev/all-hands-ai/openhands:716823f

[mamoodi]

I'm guessing this is not quite fully ready so we are waiting a bit more.