feat: probe server uptime status

[deolla]

Description

This PR introduces a new endpoint /probe to the backend, which responds with a confirmation message. The front end will use this endpoint to verify the backend's availability and response.

How should this be manually tested?

• Send a GET request to /probe.
• Verify the response is I am the express api responding.

Checklist of what you did

• Added the /probe endpoint:
• The endpoint responds with the message I am the express api responding.

Notes

The /probe endpoint is designed to confirm the backend's availability.

Reference Issues

[FEAT] Add /hng-test Page to Display Version and Backend Info #358