fix(efs): LifecyclePolicy of AFTER_7_DAYS is not applied (#9475)

Closes #9474 (see for details).

```ts
const fileSystem = new efs.FileSystem(this, "EFS", { 
      removalPolicy: cdk.RemovalPolicy.DESTROY,
      lifecyclePolicy: efs.LifecyclePolicy.AFTER_7_DAYS,
      vpc,
});
```

Old behavior:
```bash
npm run build; cdk synth | grep -r -n1 "AFTER_"; cdk diff

> demo@0.1.0 build /Users/robertd/code/demo
> tsc

Stack EFSDemoTest
Resources
[~] AWS::EFS::FileSystem EFS EFSBAA8953A
 └─ [-] LifecyclePolicies
     └─ [{"TransitionToIA":"AFTER_14_DAYS"}]
```

**New (expected) behavior:** 🎆 🥳 🍾 
```bash
npm run build; cdk synth | grep -r -n1 "AFTER_"; cdk diff

> demo@0.1.0 build /Users/robertd/demo
> tsc

(standard input)-327-      LifecyclePolicies:
(standard input):328:        - TransitionToIA: AFTER_7_DAYS
(standard input)-329-    UpdateReplacePolicy: Delete

Stack EFSDemoTest
Resources
[~] AWS::EFS::FileSystem EFS EFSBAA8953A
 └─ [~] LifecyclePolicies
     └─ @@ -1,5 +1,5 @@
        [ ] [
        [ ]   {
        [-]     "TransitionToIA": "AFTER_14_DAYS"
        [+]     "TransitionToIA": "AFTER_7_DAYS"
        [ ]   }
        [ ] ]

```

----

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

packages/@aws-cdk/aws-efs/README.md

@@ -68,7 +68,7 @@ fileSystem.connections.allowDefaultPortFrom(instance);
 
 In order to automatically mount this file system during instance launch, 
 following code can be used as reference:
-```
+```ts
 const vpc = new ec2.Vpc(this, 'VPC');
 
 const fileSystem = new efs.FileSystem(this, 'MyEfsFileSystem', {

packages/@aws-cdk/aws-efs/lib/efs-file-system.ts

@@ -13,27 +13,27 @@ export enum LifecyclePolicy {
   /**
    * After 7 days of not being accessed.
    */
-  AFTER_7_DAYS,
+  AFTER_7_DAYS = 'AFTER_7_DAYS',
 
   /**
    * After 14 days of not being accessed.
    */
-  AFTER_14_DAYS,
+  AFTER_14_DAYS = 'AFTER_14_DAYS',
 
   /**
    * After 30 days of not being accessed.
    */
-  AFTER_30_DAYS,
+  AFTER_30_DAYS = 'AFTER_30_DAYS',
 
   /**
    * After 60 days of not being accessed.
    */
-  AFTER_60_DAYS,
+  AFTER_60_DAYS = 'AFTER_60_DAYS',
 
   /**
    * After 90 days of not being accessed.
    */
-  AFTER_90_DAYS
+  AFTER_90_DAYS = 'AFTER_90_DAYS'
 }
 
 /**
@@ -247,9 +247,7 @@ export class FileSystem extends Resource implements IFileSystem {
     const filesystem = new CfnFileSystem(this, 'Resource', {
       encrypted: props.encrypted,
       kmsKeyId: (props.kmsKey ? props.kmsKey.keyId : undefined),
-      lifecyclePolicies: (props.lifecyclePolicy ? Array.of({
-        transitionToIa: LifecyclePolicy[props.lifecyclePolicy],
-      } as CfnFileSystem.LifecyclePolicyProperty) : undefined),
+      lifecyclePolicies: (props.lifecyclePolicy ? [{ transitionToIa: props.lifecyclePolicy }] : undefined),
       performanceMode: props.performanceMode,
       throughputMode: props.throughputMode,
       provisionedThroughputInMibps: props.provisionedThroughputPerSecond?.toMebibytes(),

packages/@aws-cdk/aws-efs/test/efs-file-system.test.ts

@@ -75,16 +75,16 @@ test('encrypted file system is created correctly with custom KMS', () => {
   }));
 });
 
-test('file system is created correctly with life cycle property', () => {
+test('file system is created correctly with a life cycle property', () => {
   // WHEN
   new FileSystem(stack, 'EfsFileSystem', {
     vpc,
-    lifecyclePolicy: LifecyclePolicy.AFTER_14_DAYS,
+    lifecyclePolicy: LifecyclePolicy.AFTER_7_DAYS,
   });
   // THEN
   expectCDK(stack).to(haveResource('AWS::EFS::FileSystem', {
     LifecyclePolicies: [{
-      TransitionToIA: 'AFTER_14_DAYS',
+      TransitionToIA: 'AFTER_7_DAYS',
     }],
   }));
 });