Rename trajectories_path config to save_trajectory_path

[li-boxuan]

End-user friendly description of the problem this fixes or functionality that this introduces

Breaking change: Rename trajectories_path config to save_trajectory_path

• 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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Give a summary of what the PR does, explaining any non-trivial design decisions

This is a breaking change to facilitate #6215 , which adds a new option, replay_trajectory_path. To make it clear that this existing option is used to dump/save the current trajectory, I think a renaming would be preferable.

This option is currently used by https://github.com/TheAgentCompany/TheAgentCompany/blob/2dd92500dac359a7959a4e13068452af3e2c2cce/evaluation/run_eval.py#L38 but I don't think it's widely used, since:

1. It's only documented in config doc
2. It's only used by headless mode

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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:e786c90-nikolaik   --name openhands-app-e786c90   docker.all-hands.dev/all-hands-ai/openhands:e786c90

[xingyaoww]

LGTM!