✨ 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/bdd/steps/steps.go

@@ -27,6 +27,8 @@ func InitializeAllSteps(ctx *godog.ScenarioContext, client *testserver.Client) {
 	ctx.Step(`^I request the health endpoint$`, sc.iRequestTheHealthEndpoint)
 	ctx.Step(`^the response should be "{\\"([^"]*)":\\"([^"]*)"}"$`, sc.theResponseShouldBe)
 	ctx.Step(`^the server is running$`, sc.theServerIsRunning)
+	ctx.Step(`^the server is running with v2 enabled$`, sc.theServerIsRunningWithV2Enabled)
+	ctx.Step(`^I send a POST request to v2 greet with name "([^"]*)"$`, sc.iSendPOSTRequestToV2GreetWithName)
 }
 
 func (sc *StepContext) iRequestAGreetingFor(name string) error {
@@ -59,3 +61,33 @@ func (sc *StepContext) theServerIsRunning() error {
 	// Actually verify the server is running by checking the readiness endpoint
 	return sc.client.Request("GET", "/api/ready", nil)
 }
+
+func (sc *StepContext) theServerIsRunningWithV2Enabled() error {
+	// Verify the server is running and v2 is enabled by checking v2 endpoint exists
+	// First check server is running
+	if err := sc.client.Request("GET", "/api/ready", nil); err != nil {
+		return err
+	}
+	
+	// Check if v2 endpoint is available (should return 405 Method Not Allowed for GET, which means endpoint exists)
+	// If v2 is disabled, this will return 404
+	resp, err := sc.client.CustomRequest("GET", "/api/v2/greet", nil)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	
+	// If we get 405, v2 is enabled (endpoint exists but doesn't allow GET)
+	// If we get 404, v2 is disabled
+	if resp.StatusCode == 404 {
+		return fmt.Errorf("v2 endpoint not available - v2 feature flag not enabled")
+	}
+	
+	return nil
+}
+
+func (sc *StepContext) iSendPOSTRequestToV2GreetWithName(name string) error {
+	// Create JSON request body
+	requestBody := map[string]string{"name": name}
+	return sc.client.Request("POST", "/api/v2/greet", requestBody)
+}