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.

client.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+type Client struct {
+	BaseURL    string
+	APIKey     string
+	HTTPClient *http.Client
+}
+
+func NewClient(baseURL, apiKey string) *Client {
+
+	return &Client{
+		BaseURL: baseURL,
+		APIKey:  apiKey,
+		HTTPClient: &http.Client{
+			Timeout: 30 * time.Second,
+		},
+	}
+}
+
+func (c *Client) GetSystemStatus() (*SystemStatus, error) {
+	// Create the URL for the system status endpoint.
+	url := fmt.Sprintf("%s/api/v3/system/status", c.BaseURL)
+
+	// Create a new GET request to the system status endpoint.
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+
+	// Set the API key and content type headers.
+	req.Header.Set("X-Api-Key", c.APIKey)
+	req.Header.Set("Content-Type", "application/json")
+
+	// Send the request and get the response.
+	resp, err := c.HTTPClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to send request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	// Check if the response is successful.
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to get system status: %s", resp.Status)
+	}
+
+	// Read the response body.
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read response body: %w", err)
+	}
+
+	// Unmarshal the response body into a SystemStatus struct.
+	var status SystemStatus
+	if err := json.Unmarshal(body, &status); err != nil {
+		return nil, fmt.Errorf("failed to unmarshal response body: %w", err)
+	}
+
+	// Return the SystemStatus struct.
+	return &status, nil
+}