feat: ACL labels from environment variables (#422)

* feat: add LabelService to retrieve application labels from environment variables

* feat: allow usage of labels from docker and env variables simultaneously

Prioritize labels from environment variables over labels from docker
labels

* fix: handle error returned by label_serive.go/LoadLabels

see https://github.com/steveiliop56/tinyauth/pull/422#discussion_r2443443032

* refactor(label_service): use simple loop instead of slices.ContainsFunc to avoid experimental slices package
see https://github.com/steveiliop56/tinyauth/pull/422#pullrequestreview-3354632045

* refactor: merge acl logic into one service

---------

Co-authored-by: Stavros <steveiliop56@gmail.com>

internal/controller/proxy_controller_test.go

@@ -39,6 +39,11 @@ func setupProxyController(t *testing.T, middlewares *[]gin.HandlerFunc) (*gin.En
 
 	assert.NilError(t, dockerService.Init())
 
+	// Access controls
+	accessControlsService := service.NewAccessControlsService(dockerService)
+
+	assert.NilError(t, accessControlsService.Init())
+
 	// Auth service
 	authService := service.NewAuthService(service.AuthServiceConfig{
 		Users: []config.User{
@@ -59,7 +64,7 @@ func setupProxyController(t *testing.T, middlewares *[]gin.HandlerFunc) (*gin.En
 	// Controller
 	ctrl := controller.NewProxyController(controller.ProxyControllerConfig{
 		AppURL: "http://localhost:8080",
-	}, group, dockerService, authService)
+	}, group, accessControlsService, authService)
 	ctrl.SetupRoutes()
 
 	return router, recorder, authService