feat: add YouTube engine with config file and env support

YouTube Data API v3 engine:
- Add YouTubeConfig to EnginesConfig with api_key field
- Add YOUTUBE_API_KEY env override
- Thread *config.Config through search service to factory
- Factory falls back to env vars if config fields are empty
- Update config.example.toml with youtube section

Also update default local_ported to include google and youtube.

internal/search/service.go

@@ -7,15 +7,17 @@ import (
 	"time"
 
 	"github.com/metamorphosis-dev/kafka/internal/cache"
+	"github.com/metamorphosis-dev/kafka/internal/config"
 	"github.com/metamorphosis-dev/kafka/internal/contracts"
 	"github.com/metamorphosis-dev/kafka/internal/engines"
 	"github.com/metamorphosis-dev/kafka/internal/upstream"
 )
 
 type ServiceConfig struct {
-	UpstreamURL string
-	HTTPTimeout time.Duration
-	Cache       *cache.Cache
+	UpstreamURL   string
+	HTTPTimeout   time.Duration
+	Cache         *cache.Cache
+	EnginesConfig *config.Config
 }
 
 type Service struct {
@@ -44,7 +46,7 @@ func NewService(cfg ServiceConfig) *Service {
 	return &Service{
 		upstreamClient: up,
 		planner:        engines.NewPlannerFromEnv(),
-		localEngines:  engines.NewDefaultPortedEngines(httpClient),
+		localEngines:  engines.NewDefaultPortedEngines(httpClient, cfg.EnginesConfig),
 		cache:          cfg.Cache,
 	}
 }