Source image error handling (#98)

**Issue #, if available:**
aws-controllers-k8s/community#1842

**Description of changes:**
Requeues the function reconciliation if it errors due to an image not existing. It will attempt reconciliation again after 1 minute. This allows for handling common GitOps conditions that may occur, where the function manifest is updated to use a new image URI, but the image hasn't finished pushing yet.

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

Author: jessebye

pkg/resource/function/hooks.go

@@ -16,6 +16,7 @@ package function
 import (
 	"context"
 	"errors"
+	"strings"
 	"time"
 
 	ackcompare "github.com/aws-controllers-k8s/runtime/pkg/compare"
@@ -29,15 +30,20 @@ import (
 )
 
 var (
-	ErrFunctionPending      = errors.New("Function in 'Pending' state, cannot be modified or deleted")
-	ErrCannotSetFunctionCSC = errors.New("cannot set function code signing config when package type is Image")
+	ErrFunctionPending         = errors.New("function in 'Pending' state, cannot be modified or deleted")
+	ErrSourceImageDoesNotExist = errors.New("source image does not exist")
+	ErrCannotSetFunctionCSC    = errors.New("cannot set function code signing config when package type is Image")
 )
 
 var (
 	requeueWaitWhilePending = ackrequeue.NeededAfter(
 		ErrFunctionPending,
 		5*time.Second,
 	)
+	requeueWaitWhileSourceImageDoesNotExist = ackrequeue.NeededAfter(
+		ErrSourceImageDoesNotExist,
+		1*time.Minute,
+	)
 )
 
 // isFunctionPending returns true if the supplied Lambda Function is in a pending
@@ -105,7 +111,15 @@ func (rm *resourceManager) customUpdateFunction(
 	case delta.DifferentAt("Spec.Code"):
 		err = rm.updateFunctionCode(ctx, desired, delta)
 		if err != nil {
-			return nil, err
+			// If the source image is not available, we get an error like this:
+			// "InvalidParameterValueException: Source image 1234567890.dkr.ecr.us-east-2.amazonaws.com/my-lambda:my-tag does not exist. Provide a valid source image."
+			// Because this may be recoverable (i.e. the image may be pushed once a build completes),
+			// we requeue the function for reconciliation after one minute.
+			if strings.Contains(err.Error(), "Provide a valid source image.") {
+				return nil, requeueWaitWhileSourceImageDoesNotExist
+			} else {
+				return nil, err
+			}
 		}
 	case delta.DifferentExcept(
 		"Spec.Code",