Plugins: Add termination stage to plugin loader pipeline (#72822)

* add termination stage

* uid -> pluginID (for now)

* also fix fakes

* add simple test

* Fix logger name

Co-authored-by: Giuseppe Guerra <giuseppe.guerra@grafana.com>

* inline stop func call

Co-authored-by: Giuseppe Guerra <giuseppe.guerra@grafana.com>

---------

Co-authored-by: Giuseppe Guerra <giuseppe.guerra@grafana.com>

pkg/plugins/manager/fakes/fakes.go

@@ -496,3 +496,14 @@ func (f *FakeInitializer) Initialize(ctx context.Context, ps []*plugins.Plugin)
 	}
 	return []*plugins.Plugin{}, nil
 }
+
+type FakeTerminator struct {
+	TerminateFunc func(ctx context.Context, pluginID string) error
+}
+
+func (f *FakeTerminator) Terminate(ctx context.Context, pluginID string) error {
+	if f.TerminateFunc != nil {
+		return f.TerminateFunc(ctx, pluginID)
+	}
+	return nil
+}