✨ feat: implement API v2 with feature flag control

- Added /api/v2/greet POST endpoint with JSON request/response

- Implemented ServiceV2 with Hello my friend <name>! greeting format

- Added api.v2_enabled feature flag (default: false)

- Extended BDD tests to cover v2 scenarios

- Maintained full backward compatibility with v1 API

- Added DLC_API_V2_ENABLED environment variable support

- Created ADR 0010-api-v2-feature-flag.md

- Updated configuration system to support API versioning

pkg/server/server.go

@@ -56,6 +56,14 @@ func (s *Server) setupRoutes() {
 		r.Use(s.getAllMiddlewares()...)
 		s.registerApiV1Routes(r)
 	})
+
+	// Register v2 routes if enabled
+	if s.config.GetV2Enabled() {
+		s.router.Route("/api/v2", func(r chi.Router) {
+			r.Use(s.getAllMiddlewares()...)
+			s.registerApiV2Routes(r)
+		})
+	}
 }
 
 func (s *Server) registerApiV1Routes(r chi.Router) {
@@ -66,6 +74,14 @@ func (s *Server) registerApiV1Routes(r chi.Router) {
 	})
 }
 
+func (s *Server) registerApiV2Routes(r chi.Router) {
+	greetServiceV2 := greet.NewServiceV2()
+	greetHandlerV2 := greet.NewApiV2GreetHandler(greetServiceV2)
+	r.Route("/greet", func(r chi.Router) {
+		greetHandlerV2.RegisterRoutes(r)
+	})
+}
+
 // getAllMiddlewares returns all middleware including OpenTelemetry if enabled
 func (s *Server) getAllMiddlewares() []func(http.Handler) http.Handler {
 	middlewares := []func(http.Handler) http.Handler{