Build: clean up and document integration test convention (#58170)

* clean up and document integration test convention

* clarify integration test conventions

* clean up integration tests that don't follow convention

* mark testIntegration* functions as helpers to avoid confusion

pkg/tsdb/postgres/locker_test.go

@@ -8,7 +8,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestLocker(t *testing.T) {
+func TestIntegrationLocker(t *testing.T) {
 	if testing.Short() {
 		t.Skip("Tests with Sleep")
 	}