Admin page to update server status

[ikhoon]

• A server's executor status can be updated only via the REST API in ServerStatusService. https://github.com/line/centraldogma/blob/c2d559d418e1b32130395aebb1db7d561e8fa284/server/src/main/java/com/linecorp/centraldogma/server/internal/api/sysadmin/ServerStatusService.java#L58-L67
• A server's health can't be updated externally. https://github.com/line/centraldogma/blob/3d08000d62317537f34776bfe2dbdd0621f020ca/server/src/main/java/com/linecorp/centraldogma/server/CentralDogma.java#L235

If an admin page is provided to manage the statuses, administrators can easily monitor and quickly update the statuses, saving time on operations. https://github.com/line/centraldogma/blob/efb85f5870d8204151142580087c7a35d8704cf6/webapp/src/pages/app/settings/index.tsx#L20

[minwoox]

That's going to be very useful. 👍