Add Plain HTTP Health Check Endpoint

[krapie]

What would you like to be added:

Currently, our system only has the ConnectRPC health check endpoint grpc.health.v1.Health/Check, which requires an HTTP POST request with an application/json header and an empty body. This type of health checking is not convenient for common uptime checkers, especially free 3rd-party uptime checkers.

To address this limitation, we should implement a simple Plain HTTP health check endpoint that can be accessed with an HTTP HEAD request for easier and more versatile health checking.

Why is this needed:

The current health check method is not user-friendly for common uptime checkers. Introducing a Plain HTTP health check endpoint will make it easier for users to monitor the health status of our system.

[krapie]

We need to add to also support NCP ALB. @hackerwins If we don't provide plain http health check endpoint, NCP ALB will exclude target from the load balancing target group.

실패 임계값: 정상 상태의 Target이 실패하면 비정상 상태로 전환되어 부하 분산 Target에서 제외되는 횟수

Reference: https://guide.ncloud-docs.com/docs/loadbalancer-targetgroup-vpc#2-health-check-%EC%84%A4%EC%A0%95