feat(adapi): add heartbeat api

[isamu-takagi]

Description

Add heartbeat API. https://github.com/orgs/autowarefoundation/discussions/4561

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[github-actions]

Documentation URL: https://autowarefoundation.github.io/autoware-documentation/pr-536/
Modified URLs:

• https://autowarefoundation.github.io/autoware-documentation/pr-536/design/autoware-interfaces/ad-api/features/heartbeat/
• https://autowarefoundation.github.io/autoware-documentation/pr-536/design/autoware-interfaces/ad-api/
• https://autowarefoundation.github.io/autoware-documentation/pr-536/design/autoware-interfaces/ad-api/list/api/system/heartbeat/
• https://autowarefoundation.github.io/autoware-documentation/pr-536/design/autoware-interfaces/ad-api/list/
• https://autowarefoundation.github.io/autoware-documentation/pr-536/design/autoware-interfaces/ad-api/types/autoware_adapi_v1_msgs/msg/Heartbeat/
• https://autowarefoundation.github.io/autoware-documentation/pr-536/design/autoware-interfaces/ad-api/types/
• https://autowarefoundation.github.io/autoware-documentation/pr-536/design/autoware-interfaces/ad-api/use-cases/system-monitoring/

[yukkysaito]

LGTM