Plugins: Add synchronous CDN plugin loader (#99096)

* WIP

* Run plugin validations and validation steps sequentially if feature is off

* Remove dependency between sources.Service and pluginscdn.Service

* lint

* Parallelize validation only if class is CDN

* re-generate feature toggles

* remove waitgroup usage

* PR review: Add loader concurrency limit setting

* re-generate feature toggles

* pr review feedback

* fix const name

* Skip module.js validation for cdn plugins

* do not run validation steps in parallel

* lint

* reduce diff

* re-generate feature toggles

* lint

* pr review feedback

* remove leftover config.PluginManagementCfg from sources.Service

pkg/services/pluginsintegration/loader/loader_test.go

@@ -1575,7 +1575,7 @@ func newLoader(t *testing.T, cfg *config.PluginManagementCfg, reg registry.Servi
 	terminate, err := pipeline.ProvideTerminationStage(cfg, reg, proc)
 	require.NoError(t, err)
 
-	return ProvideService(pipeline.ProvideDiscoveryStage(cfg,
+	return ProvideService(cfg, pipeline.ProvideDiscoveryStage(cfg,
 		finder.NewLocalFinder(false), reg),
 		pipeline.ProvideBootstrapStage(cfg, signature.DefaultCalculator(cfg), assets),
 		pipeline.ProvideValidationStage(cfg, signature.NewValidator(signature.NewUnsignedAuthorizer(cfg)), angularInspector),
@@ -1607,7 +1607,7 @@ func newLoaderWithOpts(t *testing.T, cfg *config.PluginManagementCfg, opts loade
 		backendFactoryProvider = fakes.NewFakeBackendProcessProvider()
 	}
 
-	return ProvideService(pipeline.ProvideDiscoveryStage(cfg,
+	return ProvideService(cfg, pipeline.ProvideDiscoveryStage(cfg,
 		finder.NewLocalFinder(false), reg),
 		pipeline.ProvideBootstrapStage(cfg, signature.DefaultCalculator(cfg), assets),
 		pipeline.ProvideValidationStage(cfg, signature.NewValidator(signature.NewUnsignedAuthorizer(cfg)), angularInspector),