Add initial implementation of *arr service client

- Created `client.go` for the main client structure and methods to interact with *arr services.
- Added `types.go` to define data structures for system status, movies, and series.
- Implemented `radarr.go` for Radarr-specific client methods including health checks and movie retrieval.
- Introduced `interfaces.go` to define service interfaces for common operations across *arr services.
- Established a basic `main.go` for application entry point.
- Included a tutorial markdown file to guide users through building the client and understanding Go concepts.
- Initialized `go.mod` for module management.
- Organized code into appropriate packages for better structure and maintainability.

main.go

@@ -0,0 +1,7 @@
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Hello, World!")
+}