Update tedge-watchdog to use the `te` MQTT topics.

[didier-wenzek]

tedge-watchdog has to be updated to:

• Use the new topic scheme
• Send health-check requests on the cmd/health/check channels of the watched services.
• Expect health status on the status/health of the the watched services.
• Be extended to run on a child device to watch the daemons running on this device. Note, that it makes no sense for tedge-watchdog to watch daemons running on a different device as the point is to restart them if not responding.

In practice:

• tedge-watchdog has to read the tedge config to get the mqtt.topic_root and its mqtt.device_topic_id. Only the services running on mqtt.device_topic_id have to be watched.
• As a first step tedge-watchdog can assume that the topic identifiers of the watched services are built using the default MQTT scheme ( device/main// -> device/main/service/tedge-agent). However, the goal is for tedge-watchdog to use an EntityStore to get the names of the services running on its device.
• This refactoring must be synchronized with the refactoring of the thin-edge daemons: as long as a service (say tedge-agent) is expecting health check on the former topic (i.e. tedge/health-check/tedge-agent), tedge-watchdog has to use this topic.

[Bravo555]

Closed by #2358

[gligorisaev]

QA has thoroughly checked the feature and here are the results:

• [x] Test for ticket exists in the test suite.
• tests/RobotFramework/tests/MQTT_health_check/MQTT_health_endpoints.robot
• tests/RobotFramework/tests/MQTT_health_check/health_tedge-mapper-collectd.robot
• tests/RobotFramework/tests/cumulocity/service_monitoring/service_monitoring.robot
• tests/RobotFramework/tests/cumulocity/software_management/software.robot
• tests/RobotFramework/tests/cumulocity/supported_operations/mapper-publishing-agent-supported-ops.robot
• tests/RobotFramework/tests/tedge/call_tedge_config_list.robot
• tests/RobotFramework/tests/tedge_to_te_converter/convert_tedge_topics_to_te_topics.robot
• tests/RobotFramework/tests/cumulocity/jwt/jwt_request.robot
• tests/RobotFramework/tests/MQTT_health_check/MQTT_health_endpoints.robot
• tests/RobotFramework/tests/MQTT_health_check/health_tedge-mapper-aws.robot
• tests/RobotFramework/tests/MQTT_health_check/health_tedge-mapper-az.robot
• tests/RobotFramework/tests/MQTT_health_check/health_tedge-mapper-collectd.robot
• [x] QA has tested the bug and could not reproduce it anymore.