add support of DOCKER_HOST_ADDR

[yuchenlin]

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

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

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

This pull request includes changes to the openhands/runtime/impl/docker/docker_runtime.py file to enhance the configuration of the Docker runtime by allowing the use of an environment variable for the Docker host address.

Configuration enhancements:

• Added import for the os module to handle environment variables.
• Modified the __init__ method to set the local_runtime_url configuration using the DOCKER_HOST_ADDR environment variable if it is present.

Mainly used for supporting some Docker-in-Docker issue when doing large-scale evaluation. Note that simply using DOCKER_HOST env var cannot enable the routing of runtime correctly.

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Link of any specific issues this addresses.
#7568