Add error message for cloning sdk timeout (#395)

Issue [#1642](aws-controllers-k8s/community#1642):

Description of changes:
add message to remind user to clone aws-go-sdk when timeout due to bad network speed 

```shell
// original
➜  code-generator git:(main) make build-controller SERVICE=ecr
building ack-generate ... ok.
==== building ecr-controller ====
Copying common custom resource definitions into ecr
Building Kubernetes API objects for ecr
Error: canot clone repository: context deadline exceeded
make: *** [build-controller] Error 1

// with new error message
➜  code-generator git:(main) ✗ make build-controller SERVICE=ecr
building ack-generate ... ok.
==== building ecr-controller ====
Copying common custom resource definitions into ecr
Building Kubernetes API objects for ecr
Error: cannot clone repository: take too long to clone sdk repo, please consider run 'git clone https://github.com/aws/aws-sdk-go' into cache dir /Users/julian/.cache/aws-controllers-k8s/src/aws-sdk-go
make: *** [build-controller] Error 1

```

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: Julian-Chu

pkg/sdk/repo.go

@@ -15,6 +15,7 @@ package sdk
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -110,15 +111,20 @@ func EnsureRepo(
 		return "", err
 	}
 
-	// Clone repository if it doen't exist
+	// Clone repository if it doesn't exist
 	sdkDir := filepath.Join(srcPath, "aws-sdk-go")
 	if _, err = os.Stat(sdkDir); os.IsNotExist(err) {
 
 		ctx, cancel := context.WithTimeout(ctx, defaultGitCloneTimeout)
 		defer cancel()
 		err = util.CloneRepository(ctx, sdkDir, sdkRepoURL)
 		if err != nil {
-			return "", fmt.Errorf("canot clone repository: %v", err)
+			// See https://github.com/aws-controllers-k8s/community/issues/1642
+			if errors.Is(err, context.DeadlineExceeded) {
+				err = fmt.Errorf("%w: take too long to clone aws sdk repo, "+
+					"please consider manually 'git clone %s' to cache dir %s", err, sdkRepoURL, sdkDir)
+			}
+			return "", fmt.Errorf("cannot clone repository: %v", err)
 		}
 	}