Implement /firestation Endpoint

[davidshin0302]

1. Task: Implement Http POST, PUT, and DELETE methods for firestation/address management.

2. Details:

• [x] POST: Add a new mapping between a firestation and an address.
• [x] PUT: Update the firestation number for an existing address.
• [x] DELETE: Remove a firestation/address mapping.

1. Suggested Steps:

• Create a service layer for managing firestation mappings.
• Implement logic to handle updates by checking the existence of an address before modifying.
• Implement methods for adding and deleting mappings.
• Create response messages for successful operations or errors.
• Write unit tests for all CRUD operations to verify correct handling.

[davidshin0302]

Completed setting up all the endpoints as wel as test casese. Jacoco reports showing above 90% from repository and controller class.