feat(docker): add ArduPilot and Gazebo environment variables

[sirinesioud-hash]

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[yeseorizi]

Maintainer follow-up applied in 0659ea6:

• kept ArduSub and Gazebo paths available to non-interactive container commands;
• removed the duplicate root shell startup hook;
• removed undefined GZ_SIM_* self-references and trailing empty path entries.

Validation: the Docker harness resolved both ardusub and sim_vehicle.py in interactive and non-interactive shells, with each PATH / Gazebo entry present exactly once. Repository pre-commit checks pass.