feat(default_ad_api): add log when operation mode change fails

[isamu-takagi]

Description

Modify error response message.
Add warn log to guide user to GUI tool.

Tests performed

1. Launch planning simulation.
2. Request to change to autonomous mode without setting pose and goal.

ros2 service call /api/operation_mode/change_to_autonomous autoware_adapi_v1_msgs/srv/ChangeOperationMode

Effects on system behavior

Not applicable.

Interface changes

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[TakaHoribe]

Worked as expected:

[stale]

This pull request has been automatically marked as stale because it has not had recent activity.

missed

[yukkysaito]

@isamu-takagi Will you merge this or close it?

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[isamu-takagi]

For some reason, the difference of this PR were included in #7432, so I will close it.