docs: add pull over description for fail-safe doc

[asana17]

Description

Added a description of pull over MRM to the fail-safe doc.

Related Links

autowarefoundation/autoware_adapi_msgs#43

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[github-actions]

Documentation URL: https://autowarefoundation.github.io/autoware-documentation/pr-461/
Modified URLs:

• https://autowarefoundation.github.io/autoware-documentation/pr-461/design/autoware-interfaces/ad-api/features/fail-safe/

[stale]

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