chore(ec2): enforceSSL on flowLog s3 bucket (#18271)

could pass another bucket, but automatically created buckets are convenient/popular, so worth improving defaults

https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-ec2.FlowLog.html
https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-s3.Bucket.html

---

```sh
# updated integ snapshots
packages/@aws-cdk/aws-ec2 $ /workspace/aws-cdk/tools/\@aws-cdk/cdk-integ-tools/bin/cdk-integ --dry-run
```

----

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

Author: PatMyron

packages/@aws-cdk/aws-ec2/lib/vpc-flow-logs.ts

@@ -198,6 +198,7 @@ class S3Destination extends FlowLogDestination {
     if (this.props.s3Bucket === undefined) {
       s3Bucket = new s3.Bucket(scope, 'Bucket', {
         encryption: s3.BucketEncryption.UNENCRYPTED,
+        enforceSSL: true,
         removalPolicy: RemovalPolicy.RETAIN,
       });
     } else {

packages/@aws-cdk/aws-ec2/test/integ.vpc-flow-logs.expected.json

@@ -527,6 +527,53 @@
       "UpdateReplacePolicy": "Retain",
       "DeletionPolicy": "Retain"
     },
+    "VPCFlowLogsS3BucketPolicyB2C2A045": {
+      "Type": "AWS::S3::BucketPolicy",
+      "Properties": {
+        "Bucket": {
+          "Ref": "VPCFlowLogsS3BucketFB7DC2BE"
+        },
+        "PolicyDocument": {
+          "Statement": [
+            {
+              "Action": "s3:*",
+              "Condition": {
+                "Bool": {
+                  "aws:SecureTransport": "false"
+                }
+              },
+              "Effect": "Deny",
+              "Principal": {
+                "AWS": "*"
+              },
+              "Resource": [
+                {
+                  "Fn::GetAtt": [
+                    "VPCFlowLogsS3BucketFB7DC2BE",
+                    "Arn"
+                  ]
+                },
+                {
+                  "Fn::Join": [
+                    "",
+                    [
+                      {
+                        "Fn::GetAtt": [
+                          "VPCFlowLogsS3BucketFB7DC2BE",
+                          "Arn"
+                        ]
+                      },
+                      "/*"
+                    ]
+                  ]
+                }
+              ]
+            }
+          ],
+          "Version": "2012-10-17"
+        }
+      }
+    },
     "VPCFlowLogsS3FlowLogB5256CFF": {
       "Type": "AWS::EC2::FlowLog",
       "Properties": {