Add Dog Handler Endpoint

Summary

This PR adds a new /api/dog endpoint to the animals API service that randomly returns either "woof" or "bark" when called.

Changes

Added new DogHandler with randomization logic
Implemented handler tests for the dog endpoint
Updated README with new endpoint documentation
Extended routing configuration to include dog endpoint

Technical Details

Uses math/rand for sound randomization
Follows existing handler pattern with BaseHandler embedding
Includes comprehensive test coverage for the new endpoint
Unique response format that returns only the sound (differs from other handlers)

Testing

Added unit tests for all DogHandler functionality
Verified random sound generation
Tested HTTP method restrictions
Endpoint can be tested locally using: curl http://localhost:8080/api/dog