feat: Add Terraform provider main entry point with schema definition and resource/data source registration

- Add main function with plugin.Serve to initialize Terraform provider plugin
- Add Provider function returning schema.Provider with api_url and api_key configuration
- Add api_url schema with TELECOM_API_URL environment variable fallback to http://localhost:8000
- Add api_key schema with TELECOM_API_KEY environment variable, marked as sensitive and optional
- Register resources: telecom_subscriber and

terraform/provider/main.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/plugin"
+)
+
+func main() {
+	plugin.Serve(&plugin.ServeOpts{
+		ProviderFunc: Provider,
+	})
+}
+
+func Provider() *schema.Provider {
+	return &schema.Provider{
+		Schema: map[string]*schema.Schema{
+			"api_url": {
+				Type:        schema.TypeString,
+				Required:    true,
+				DefaultFunc: schema.EnvDefaultFunc("TELECOM_API_URL", "http://localhost:8000"),
+				Description: "The base URL of the Telecom API server.",
+			},
+			"api_key": {
+				Type:        schema.TypeString,
+				Optional:    true,
+				Sensitive:   true,
+				DefaultFunc: schema.EnvDefaultFunc("TELECOM_API_KEY", nil),
+				Description: "API key for authenticating with the Telecom API.",
+			},
+		},
+		ResourcesMap: map[string]*schema.Resource{
+			"telecom_subscriber": resourceSubscriber(),
+			"telecom_rating_plan": resourceRatingPlan(),
+		},
+		DataSourcesMap: map[string]*schema.Resource{
+			"telecom_subscriber":  dataSourceSubscriber(),
+			"telecom_system_stats": dataSourceSystemStats(),
+		},
+		ConfigureContextFunc: providerConfigure,
+	}
+}