test(e2e): add ability to skip building docker image

This allows you to run e2e tests without rebuilding the image by setting
E2E_SKIP_BUILD environment variable.

Signed-off-by: Adam Reese <adam@reese.io>

e2e/main_test.go

@@ -48,9 +48,10 @@ func TestMain(m *testing.M) {
 
 		// build and load spin operator image into cluster
 		func(ctx context.Context, _ *envconf.Config) (context.Context, error) {
-			if p := utils.RunCommand(`bash -c "cd .. && IMG=ghcr.io/spinkube/spin-operator:dev make docker-build"`); p.Err() != nil {
-
-				return ctx, fmt.Errorf(ErrFormat, p.Err(), p.Out())
+			if os.Getenv("E2E_SKIP_BUILD") == "" { // nolint:forbidigo
+				if p := utils.RunCommand(`bash -c "cd .. && IMG=ghcr.io/spinkube/spin-operator:dev make docker-build"`); p.Err() != nil {
+					return ctx, fmt.Errorf(ErrFormat, p.Err(), p.Out())
+				}
 			}
 
 			if p := utils.RunCommand(("k3d image import -c " + cluster.name + " ghcr.io/spinkube/spin-operator:dev")); p.Err() != nil {