Add combined health check endpoint which can check multiple components

[iprentic]

So far, only checks ElasticSearch client, the first one we implemented

Example response on quickstart for URL: http://localhost:8080/health/check/combined

200 response with body

{"elastic":{"headers":{},"body":"{\"cluster_name\":\"docker-cluster\",\"status\":\"yellow\",\"timed_out\":false,\"number_of_nodes\":1,\"number_of_data_nodes\":1,\"active_primary_shards\":65,\"active_shards\":65,\"relocating_shards\":0,\"initializing_shards\":0,\"unassigned_shards\":62,\"delayed_unassigned_shards\":0,\"number_of_pending_tasks\":0,\"number_of_in_flight_fetch\":0,\"task_max_waiting_in_queue_millis\":0,\"active_shards_percent_as_number\":51.181102362204726}","statusCodeValue":200,"statusCode":"OK"}}

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[david-leifker]

Couple minor comments, once this gets into a release lets be sure update the readiness probe here and make sure it works as expected.

[iprentic]

Example usages:

Base endpoint: http://localhost:8080/health/check/ready
Status code: 200

{"elasticsearch":{"headers":{},"body":"{\"cluster_name\":\"docker-cluster\",\"status\":\"yellow\",\"timed_out\":false,\"number_of_nodes\":1,\"number_of_data_nodes\":1,\"active_primary_shards\":65,\"active_shards\":65,\"relocating_shards\":0,\"initializing_shards\":0,\"unassigned_shards\":62,\"delayed_unassigned_shards\":0,\"number_of_pending_tasks\":0,\"number_of_in_flight_fetch\":0,\"task_max_waiting_in_queue_millis\":0,\"active_shards_percent_as_number\":51.181102362204726}","statusCodeValue":200,"statusCode":"OK"}}

Check Elastic component explicitly: http://localhost:8080/health/check/ready?checks=elasticsearch
Same response as above.

Check non-existent component: http://localhost:8080/health/check/ready?checks=hello
Status code: 500

{"hello":{"headers":{},"body":"Unrecognized component hello","statusCodeValue":500,"statusCode":"INTERNAL_SERVER_ERROR"}}

Check existent and non-existent component: http://localhost:8080/health/check/ready?checks=hello,elasticsearch
Status code: 500

{"elasticsearch":{"headers":{},"body":"{\"cluster_name\":\"docker-cluster\",\"status\":\"yellow\",\"timed_out\":false,\"number_of_nodes\":1,\"number_of_data_nodes\":1,\"active_primary_shards\":65,\"active_shards\":65,\"relocating_shards\":0,\"initializing_shards\":0,\"unassigned_shards\":62,\"delayed_unassigned_shards\":0,\"number_of_pending_tasks\":0,\"number_of_in_flight_fetch\":0,\"task_max_waiting_in_queue_millis\":0,\"active_shards_percent_as_number\":51.181102362204726}","statusCodeValue":200,"statusCode":"OK"},"hello":{"headers":{},"body":"Unrecognized component hello","statusCodeValue":500,"statusCode":"INTERNAL_SERVER_ERROR"}}