Refactor configuration management and enhance build process

- Introduced a YAML-based configuration system, allowing for automatic generation of a default `config.yaml` file.
- Updated the application to load configuration settings from the YAML file, improving flexibility and ease of use.
- Added a Makefile to streamline development tasks, including running the application, testing, and managing dependencies.
- Enhanced `.gitignore` to include build artifacts and configuration files.
- Removed unused Prometheus metrics and related code to simplify the codebase.
- Updated dependencies in `go.mod` and `go.sum` for improved functionality and performance.

Makefile

@@ -0,0 +1,19 @@
+run: deps test ## Run the application
+	@go run .
+
+help: ## Show this help message
+	@echo SteamCache2 Makefile
+	@echo Available targets:
+	@echo   run                Run the application
+	@echo   run-debug          Run the application with debug logging
+	@echo   test               Run all tests
+	@echo   deps               Download dependencies
+
+run-debug: deps test ## Run the application with debug logging
+	@go run . --log-level debug
+
+test: deps ## Run all tests
+	@go test -v ./...
+
+deps: ## Download dependencies
+	@go mod tidy